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Sample records for induced insulin secretion

  1. Peroxiredoxin 4 Improves Insulin Biosynthesis and Glucose-induced Insulin Secretion in Insulin-secreting INS-1E Cells*

    PubMed Central

    Mehmeti, Ilir; Lortz, Stephan; Elsner, Matthias; Lenzen, Sigurd

    2014-01-01

    Oxidative folding of (pro)insulin is crucial for its assembly and biological function. This process takes place in the endoplasmic reticulum (ER) and is accomplished by protein disulfide isomerase and ER oxidoreductin 1β, generating stoichiometric amounts of hydrogen peroxide (H2O2) as byproduct. During insulin resistance in the prediabetic state, increased insulin biosynthesis can overwhelm the ER antioxidative and folding capacity, causing an imbalance in the ER redox homeostasis and oxidative stress. Peroxiredoxin 4 (Prdx4), an ER-specific antioxidative peroxidase can utilize luminal H2O2 as driving force for reoxidizing protein disulfide isomerase family members, thus efficiently contributing to disulfide bond formation. Here, we examined the functional significance of Prdx4 on β-cell function with emphasis on insulin content and secretion during stimulation with nutrient secretagogues. Overexpression of Prdx4 in glucose-responsive insulin-secreting INS-1E cells significantly metabolized luminal H2O2 and improved the glucose-induced insulin secretion, which was accompanied by the enhanced proinsulin mRNA transcription and insulin content. This β-cell beneficial effect was also observed upon stimulation with the nutrient insulin secretagogue combination of leucine plus glutamine, indicating that the effect is not restricted to glucose. However, knockdown of Prdx4 had no impact on H2O2 metabolism or β-cell function due to the fact that Prdx4 expression is negligibly low in pancreatic β-cells. Moreover, we provide evidence that the constitutively low expression of Prdx4 is highly susceptible to hyperoxidation in the presence of high glucose. Overall, these data suggest an important role of Prdx4 in maintaining insulin levels and improving the ER folding capacity also under conditions of a high insulin requirement. PMID:25122762

  2. Macrophage-secreted factors induce adipocyte inflammation and insulin resistance

    SciTech Connect

    Permana, Paska A. . E-mail: Paska.Permana@med.va.gov; Menge, Christopher; Reaven, Peter D.

    2006-03-10

    Macrophage infiltration into adipose tissue increases with obesity, a condition associated with low-grade inflammation and insulin resistance. We investigated the direct effects of macrophage-secreted factors on adipocyte inflammation and insulin resistance. 3T3-L1 adipocytes incubated with media conditioned by RAW264.7 macrophages (RAW-CM) showed dramatically increased transcription of several inflammation-related genes, greater nuclear factor kappa B (NF-{kappa}B) activity, and enhanced binding of U937 monocytes. All of these effects were prevented by co-incubation with pyrrolidinedithiocarbamate, an NF-{kappa}B inhibitor. Adipocytes incubated with RAW-CM also released more non-esterified fatty acids and this increased lipolysis was not suppressed by insulin. In addition, RAW-CM treatment decreased insulin-stimulated glucose uptake in adipocytes. Taken together, these results indicate that macrophage-secreted factors induce inflammatory responses and reduce insulin responsiveness in adipocytes. These effects of macrophage-secreted factors on adipocytes may contribute significantly to the systemic inflammation and insulin resistance associated with obesity.

  3. Impairment of GLP1-induced insulin secretion: role of genetic background, insulin resistance and hyperglycaemia.

    PubMed

    Herzberg-Schäfer, S; Heni, M; Stefan, N; Häring, H-U; Fritsche, A

    2012-10-01

    One major risk factor of type 2 diabetes is the impairment of glucose-induced insulin secretion which is mediated by the individual genetic background and environmental factors. In addition to impairment of glucose-induced insulin secretion, impaired glucagon-like peptide (GLP)1-induced insulin secretion has been identified to be present in subjects with diabetes and impaired glucose tolerance, but little is known about its fundamental mechanisms. The state of GLP1 resistance is probably an important mechanism explaining the reduced incretin effect observed in type 2 diabetes. In this review, we address methods that can be used for the measurement of insulin secretion in response to GLP1 in humans, and studies showing that specific diabetes risk genes are associated with resistance of the secretory function of the β-cell in response to GLP1 administration. Furthermore, we discuss other factors that are associated with impaired GLP1-induced insulin secretion, for example, insulin resistance. Finally, we provide evidence that hyperglycaemia per se, the genetic background and their interaction result in the development of GLP1 resistance of the β-cell. We speculate that the response or the non-response to therapy with GLP1 analogues and/or dipeptidyl peptidase-4 (DPP-IV) inhibitors is critically dependent on GLP1 resistance.

  4. Effect of Naloxon on Counter Insulin Hormone Secretion in Insulin-Induced Hypoglycemia

    PubMed Central

    Ju, Yeong Shil; Kim, Sung Woon; Yang, In Myung; Kim, Jin Woo; Kim, Young Seol; Choi, Young Kil

    1987-01-01

    To investigate the normal physiologic role of endogenous opiates in glucose homeostasis and as a preliminary study for clarifying the association of endogenous opites with pathophysilogy of NIDDM, we obseved the changes in the secretion of counter-insulin hormones in response to insulin-induced hypoglycemia with or without naloxone. The results were as follows: Blood glucose was decreased significantly more rapidly with naloxone infusion than after insulin alone, which seems to play a role in the early responses of ACTH and GH.Not only was the more rapid response of ACTH and GH, but also the prolonged secretion of ACTH and Cortisol were observed after administration of insulin and naloxone. We concluded that endogenous opiates may be involved in the feedback regulation of secretion of ACTH and GH during hypoglycemia either at hypophysis or hypothalamus, and involved in glucose homeostasis via a certain direct mechanism other than regulation of counter hormone secretion. PMID:2856480

  5. Studies on the mechanism of salicylate-induced increase of insulin secretion in man.

    PubMed

    Giugliano, D; Cozzolino, D; Ceriello, A; Cerciello, T; Varano, R; Saccomanno, F; Torella, R

    1988-01-01

    Salicylate compounds are known to increase basal and stimulated insulin secretion in man. In our studies, infusion of lysine acetylsalicylate (72 mg/min) increased basal insulin levels and amplified insulin responses to glucose (5 g i.v.), arginine (5 g i.v.) and tolbutamide (1 g i.v.). Verapamil, an organic calcium antagonist, did not modify LAS-induced increase of basal insulin levels, but reduced the effect of LAS on glucose-induced insulin secretion. Calcitonin and somatostatin, two agents that inhibit basal and glucose-stimulated insulin secretion, inhibited the insulin response to glucose in presence of LAS infusion. The ability of salicylate compounds to augment insulin secretion might be due to multiple sites of action in the Beta-cells.

  6. Investigation of morin-induced insulin secretion in cultured pancreatic cells.

    PubMed

    Lin, Mang Hung; Hsu, Chia-Chen; Lin, Jenshinn; Cheng, Juei Tang; Wu, Ming Chang

    2017-07-12

    Morin is a flavonoid contained in guava that is known to reduce hyperglycemia in diabetes. Insulin secretion has been demonstrated to increase following the administration of morin. The present study is designed to investigate the potential mechanism(s) of morin-induced insulin secretion in the MIN6 cell line. First, we identified that morin induced a dose-dependent increase in insulin secretion and intracellular calcium content in MIN6 cells. Morin potentiated glucose-stimulated insulin secretion (GSIS). Additionally, we used siRNA for the ablation of imidazoline receptor protein (NISCH) expression in MIN6 cells. Interestingly, the effects of increased insulin secretion by morin and canavanine were markedly reduced in Si-NISCH cells. Moreover, we used KU14R to block imidazoline I3 receptor (I-3R) that is known to enhance insulin release from the pancreatic β-cells. Without influence on the basal insulin secretion, KU14R dose-dependently inhibited the increased insulin secretion induced by morin or efaroxan in MIN6 cells. Additionally, effects of increased insulin secretion by morin or efaroxan were reduced by diazoxide at the dose sufficient to open KATP channels and attenuated by nifedipine at the dose used to inhibit L-type calcium channels. Otherwise, phospholipase C (PLC) is introduced to couple with imidazoline receptor (I-R). The PLC inhibitor dose-dependently inhibited the effects of morin in MIN6 cells. Similar blockade was also observed in protein kinase C (PKC) inhibitor-treated cells. Taken together, we found that morin increases insulin secretion via the activation of I-R in pancreatic cells. Therefore, morin would be useful to develop in the research and treatment of diabetic disorders. © 2017 John Wiley & Sons Australia, Ltd.

  7. Functional Role of Serotonin in Insulin Secretion in a Diet-Induced Insulin-Resistant State

    PubMed Central

    Kim, Kyuho; Oh, Chang-Myung; Ohara-Imaizumi, Mica; Park, Sangkyu; Namkung, Jun; Yadav, Vijay K.; Tamarina, Natalia A.; Roe, Michael W.; Philipson, Louis H.; Karsenty, Gerard; Nagamatsu, Shinya

    2015-01-01

    The physiological role of serotonin, or 5-hydroxytryptamine (5-HT), in pancreatic β-cell function was previously elucidated using a pregnant mouse model. During pregnancy, 5-HT increases β-cell proliferation and glucose-stimulated insulin secretion (GSIS) through the Gαq-coupled 5-HT2b receptor (Htr2b) and the 5-HT3 receptor (Htr3), a ligand-gated cation channel, respectively. However, the role of 5-HT in β-cell function in an insulin-resistant state has yet to be elucidated. Here, we characterized the metabolic phenotypes of β-cell-specific Htr2b−/− (Htr2b βKO), Htr3a−/− (Htr3a knock-out [KO]), and β-cell-specific tryptophan hydroxylase 1 (Tph1)−/− (Tph1 βKO) mice on a high-fat diet (HFD). Htr2b βKO, Htr3a KO, and Tph1 βKO mice exhibited normal glucose tolerance on a standard chow diet. After 6 weeks on an HFD, beginning at 4 weeks of age, both Htr3a KO and Tph1 βKO mice developed glucose intolerance, but Htr2b βKO mice remained normoglycemic. Pancreas perfusion assays revealed defective first-phase insulin secretion in Htr3a KO mice. GSIS was impaired in islets isolated from HFD-fed Htr3a KO and Tph1 βKO mice, and 5-HT treatment improved insulin secretion from Tph1 βKO islets but not from Htr3a KO islets. Tph1 and Htr3a gene expression in pancreatic islets was not affected by an HFD, and immunostaining could not detect 5-HT in pancreatic islets from mice fed an HFD. Taken together, these results demonstrate that basal 5-HT levels in β-cells play a role in GSIS through Htr3, which becomes more evident in a diet-induced insulin-resistant state. PMID:25426873

  8. Mechanisms of p-methoxycinnamic acid-induced increase in insulin secretion.

    PubMed

    Adisakwattana, S; Hsu, W H; Yibchok-anun, S

    2011-10-01

    p-Methoxycinnamic acid (p-MCA) is a cinnamic acid derivative that shows various pharmacologic actions such as hepatoprotective and antihyperglycemic activities. The present study was to elucidate the mechanisms by which p-MCA increases [Ca²⁺]i and insulin secretion in INS-1 cells. p-MCA (100 μM) increased [Ca²⁺]i in INS-1 cells. The p-MCA-induced insulin secretion and rise in [Ca²⁺]i were markedly inhibited in the absence of extracellular Ca²⁺ or in the presence of an L-type Ca²⁺ channel blocker nimodipine. These results suggested that p-MCA increased Ca²⁺ influx via the L-type Ca²⁺ channels. Diazoxide, an ATP-sensitive K⁺ channel opener, did not alter p-MCA-induced insulin secretion, nor [Ca²⁺]i response. In addition, p-MCA enhanced glucose-, glibenclamide-induced insulin secretion whereas it also potentiated the increase in insulin secretion induced by arginine, and Bay K 8644, an L-type Ca²⁺ channel agonist. Taken together, our results suggest that p-MCA stimulated insulin secretion from pancreatic β-cells by increasing Ca²⁺ influx via the L-type Ca²⁺ channels, but not through the closure of ATP-sensitive K⁺ channels.

  9. Adiponectin increases glucose-induced insulin secretion through the activation of lipid oxidation.

    PubMed

    Patané, G; Caporarello, N; Marchetti, P; Parrino, C; Sudano, D; Marselli, L; Vigneri, R; Frittitta, L

    2013-12-01

    The expression of adiponectin receptors has been demonstrated in human and rat pancreatic beta cells, where globular (g) adiponectin rescues rat beta cells from cytokine and fatty acid-induced apoptosis. The aim of our study was to evaluate whether adiponectin has a direct effect on insulin secretion and the metabolic pathways involved. Purified human pancreatic islets and rat beta cells (INS-1E) were exposed (1 h) to g-adiponectin, and glucose-induced insulin secretion was measured. A significant increase in glucose-induced insulin secretion was observed in the presence of g-adiponectin (1 nmol/l) with respect to control cells in both human pancreatic islets (n = 5, p < 0.05) and INS-1E cells (n = 5, p < 0.001). The effect of globular adiponectin on insulin secretion was independent of AMP-dependent protein kinase (AMPK) activation or glucose oxidation. In contrast, g-adiponectin significantly increased oleate oxidation (n = 5, p < 0.05), and the effect of g-adiponectin (p < 0.001) on insulin secretion by INS-1E was significantly reduced in the presence of etomoxir (1 μmol/l), an inhibitor of fatty acid beta oxidation. g-Adiponectin potentiates glucose-induced insulin secretion in both human pancreatic islets and rat beta cells via an AMPK independent pathway. Increased fatty acid oxidation rather than augmented glucose oxidation is the mechanism responsible. Overall, our data indicate that, in addition to its anti-apoptotic action, g-adiponectin has another direct effect on beta cells by potentiating insulin secretion. Adiponectin, therefore, in addition to its well-known effect on insulin sensitivity, has important effects at the pancreatic level.

  10. Enhanced insulin secretion and insulin sensitivity in young lambs with placental insufficiency-induced intrauterine growth restriction.

    PubMed

    Camacho, Leticia E; Chen, Xiaochuan; Hay, William W; Limesand, Sean W

    2017-08-01

    Intrauterine growth restriction (IUGR) is associated with persistent metabolic complications, but information is limited for IUGR infants. We determined glucose-stimulated insulin secretion (GSIS) and insulin sensitivity in young lambs with placental insufficiency-induced IUGR. Lambs with hyperthermia-induced IUGR (n = 7) were compared with control lambs (n = 8). GSIS was measured at 8 ± 1 days of age, and at 15 ± 1 days, body weight-specific glucose utilization rates were measured with radiolabeled d-glucose during a hyperinsulinemic-euglycemic clamp (HEC). IUGR lambs weighed 23% less (P < 0.05) than controls at birth. Fasting plasma glucose and insulin concentrations were not different between IUGR and controls for either study. First-phase insulin secretion was enhanced 2.3-fold in IUGR lambs compared with controls. However, second-phase insulin concentrations, glucose-potentiated arginine-stimulated insulin secretion, and β-cell mass were not different, indicating that IUGR β-cells have an intrinsic enhancement in acute GSIS. Compared with controls, IUGR lambs had higher body weight-specific glucose utilization rates and greater insulin sensitivity at fasting (1.6-fold) and hyperinsulinemic periods (2.4-fold). Improved insulin sensitivity for glucose utilization was not due to differences in skeletal muscle insulin receptor and glucose transporters 1 and 4 concentrations. Plasma lactate concentrations during HEC were elevated in IUGR lambs compared with controls, but no differences were found for glycogen content or citrate synthase activity in liver and muscle. Greater insulin sensitivity for glucose utilization and enhanced acute GSIS in young lambs are predicted from fetal studies but may promote conditions that exaggerate glucose disposal and lead to episodes of hypoglycemia in IUGR infants. Copyright © 2017 the American Physiological Society.

  11. Pregnancy restores insulin secretion from pancreatic islets in cafeteria diet-induced obese rats.

    PubMed

    Vanzela, E C; Ribeiro, R A; de Oliveira, C A Machado; Rodrigues, F B; Bonfleur, M L; Carneiro, E M; Souza, K L A; Boschero, A C

    2010-02-01

    Insulin resistance during pregnancy is counteracted by enhanced insulin secretion. This condition is aggravated by obesity, which increases the risk of gestational diabetes. Therefore, pancreatic islet functionality was investigated in control nonpregnant (C) and pregnant (CP), and cafeteria diet-fed nonpregnant (Caf), and pregnant (CafP) obese rats. Isolated islets were used for measurements of insulin secretion (RIA), NAD(P)H production (MTS), glucose oxidation ((14)CO(2) production), intracellular Ca(2+) levels (fura-2 AM), and gene expression (real-time PCR). Impaired glucose tolerance was clearly established in Caf and CafP rats at the 14th wk on a diet. Insulin secretion induced by direct depolarizing agents such as KCl and tolbutamide and increasing concentrations of glucose was significantly reduced in Caf, compared with C islets. This reduction was not observed in islets from CP and CafP rats. Accordingly, the glucose oxidation and production of reduced equivalents were increased in CafP islets. The glucose-induced Ca(2+) increase was significantly lower in Caf and higher in CafP, compared with all other groups. CP and CafP islets demonstrated an increased Ca(2+) oscillation frequency, compared with both C and Caf islets, and the amplitude of oscillations was augmented in CafP, compared with Caf islets. In addition, Ca(v)alpha1.2 and SERCA2a mRNA levels were reduced in Caf islets. Ca(v)alpha1.2, but not SERCA2a, mRNA was normalized in CafP islets. In conclusion, cafeteria diet-induced obesity impairs insulin secretion. This alteration is related to the impairment of Ca(2+) handling in pancreatic islets, in especial Ca(2+) influx, a defect that is reversed during pregnancy allowing normalization of insulin secretion.

  12. Nicotinamide induces differentiation of embryonic stem cells into insulin-secreting cells

    SciTech Connect

    Vaca, Pilar; Berna, Genoveva; Araujo, Raquel; Carneiro, Everardo M.; Bedoya, Francisco J.; Soria, Bernat; Martin, Franz

    2008-03-10

    The poly(ADP-ribose) polymerase (PARP) inhibitor, nicotinamide, induces differentiation and maturation of fetal pancreatic cells. In addition, we have previously reported evidence that nicotinamide increases the insulin content of cells differentiated from embryonic stem (ES) cells, but the possibility of nicotinamide acting as a differentiating agent on its own has never been completely explored. Islet cell differentiation was studied by: (i) X-gal staining after neomycin selection; (ii) BrdU studies; (iii) single and double immunohistochemistry for insulin, C-peptide and Glut-2; (iv) insulin and C-peptide content and secretion assays; and (v) transplantation of differentiated cells, under the kidney capsule, into streptozotocin (STZ)-diabetic mice. Here we show that undifferentiated mouse ES cells treated with nicotinamide: (i) showed an 80% decrease in cell proliferation; (ii) co-expressed insulin, C-peptide and Glut-2; (iii) had values of insulin and C-peptide corresponding to 10% of normal mouse islets; (iv) released insulin and C-peptide in response to stimulatory glucose concentrations; and (v) after transplantation into diabetic mice, normalized blood glucose levels over 7 weeks. Our data indicate that nicotinamide decreases ES cell proliferation and induces differentiation into insulin-secreting cells. Both aspects are very important when thinking about cell therapy for the treatment of diabetes based on ES cells.

  13. p16(Ink4a)-induced senescence of pancreatic beta cells enhances insulin secretion.

    PubMed

    Helman, Aharon; Klochendler, Agnes; Azazmeh, Narmen; Gabai, Yael; Horwitz, Elad; Anzi, Shira; Swisa, Avital; Condiotti, Reba; Granit, Roy Z; Nevo, Yuval; Fixler, Yaakov; Shreibman, Dorin; Zamir, Amit; Tornovsky-Babeay, Sharona; Dai, Chunhua; Glaser, Benjamin; Powers, Alvin C; Shapiro, A M James; Magnuson, Mark A; Dor, Yuval; Ben-Porath, Ittai

    2016-04-01

    Cellular senescence is thought to contribute to age-associated deterioration of tissue physiology. The senescence effector p16(Ink4a) is expressed in pancreatic beta cells during aging and limits their proliferative potential; however, its effects on beta cell function are poorly characterized. We found that beta cell-specific activation of p16(Ink4a) in transgenic mice enhances glucose-stimulated insulin secretion (GSIS). In mice with diabetes, this leads to improved glucose homeostasis, providing an unexpected functional benefit. Expression of p16(Ink4a) in beta cells induces hallmarks of senescence--including cell enlargement, and greater glucose uptake and mitochondrial activity--which promote increased insulin secretion. GSIS increases during the normal aging of mice and is driven by elevated p16(Ink4a) activity. We found that islets from human adults contain p16(Ink4a)-expressing senescent beta cells and that senescence induced by p16(Ink4a) in a human beta cell line increases insulin secretion in a manner dependent, in part, on the activity of the mechanistic target of rapamycin (mTOR) and the peroxisome proliferator-activated receptor (PPAR)-γ proteins. Our findings reveal a novel role for p16(Ink4a) and cellular senescence in promoting insulin secretion by beta cells and in regulating normal functional tissue maturation with age.

  14. PPARalpha suppresses insulin secretion and induces UCP2 in insulinoma cells.

    PubMed

    Tordjman, Karen; Standley, Kara N; Bernal-Mizrachi, Carlos; Leone, Teresa C; Coleman, Trey; Kelly, Daniel P; Semenkovich, Clay F

    2002-06-01

    Fatty acids may promote type 2 diabetes by altering insulin secretion from pancreatic beta cells, a process known as lipotoxicity. The underlying mechanisms are poorly understood. To test the hypothesis that peroxisome proliferator-activated receptor alpha (PPARalpha) has a direct effect on islet function, we treated INS-1 cells, an insulinoma cell line, with a PPARalpha adenovirus (AdPPARalpha) as well as the PPARalpha agonist clofibric acid. AdPPARalpha-infected INS-1 cells showed PPARalpha agonist- and fatty acid-dependent transactivation of a PPARalpha reporter gene. Treatment with either AdPPARalpha or clofibric acid increased both catalase activity (a marker of peroxisomal proliferation) and palmitate oxidation. AdPPARalpha induced carnitine-palmitoyl transferase-I (CPT-I) mRNA, but had no effect on insulin gene expression. AdPPARalpha treatment increased cellular triglyceride content but clofibric acid did not. Both AdPPARalpha and clofibric acid decreased basal and glucose-stimulated insulin secretion. Despite increasing fatty acid oxidation, AdPPARalpha did not increase cellular ATP content suggesting the stimulation of uncoupled respiration. Consistent with these observations, UCP2 expression doubled in PPARalpha-treated cells. Clofibric acid-induced suppression of glucose-simulated insulin secretion was prevented by the CPT-I inhibitor etomoxir. These data suggest that PPARalpha-stimulated fatty acid oxidation can impair beta cell function.

  15. Assessment of benzene induced oxidative impairment in rat isolated pancreatic islets and effect on insulin secretion.

    PubMed

    Bahadar, Haji; Maqbool, Faheem; Mostafalou, Sara; Baeeri, Maryam; Rahimifard, Mahban; Navaei-Nigjeh, Mona; Abdollahi, Mohammad

    2015-05-01

    Benzene (C6H6) is an organic compound used in petrochemicals and numerous other industries. It is abundantly released to our environment as a chemical pollutant causing widespread human exposure. This study mainly focused on benzene induced toxicity on rat pancreatic islets with respect to oxidative damage, insulin secretion and glucokinase (GK) activity. Benzene was dissolved in corn oil and administered orally at doses 200, 400 and 800mg/kg/day, for 4 weeks. In rats, benzene significantly raised the concentration of plasma insulin. Also the effect of benzene on the release of glucose-induced insulin was pronounced in isolated islets. Benzene caused oxidative DNA damage and lipid peroxidation, and also reduced the cell viability and total thiols groups, in the islets of exposed rats. In conclusion, the current study revealed that pancreatic glucose metabolism is susceptible to benzene toxicity and the resultant oxidative stress could lead to functional abnormalities in the pancreas.

  16. Combined contributions of over-secreted glucagon-like peptide 1 and suppressed insulin secretion to hyperglycemia induced by gatifloxacin in rats

    SciTech Connect

    Yu, Yunli; Wang, Xinting; Liu, Can; Yao, Dan; Hu, Mengyue; Li, Jia; Hu, Nan; Liu, Li; Liu, Xiaodong

    2013-02-01

    Accumulating evidences have showed that gatifloxacin causes dysglycemia in both diabetic and non-diabetic patients. Our preliminary study demonstrated that gatifloxacin stimulated glucagon-like peptide 1 (GLP-1) secretion from intestinal cells. The aim of the study was to investigate the association between gatifloxacin-stimulated GLP-1 release and dysglycemia in both normal and streptozotocin-induced diabetic rats and explore the possible mechanisms. Oral administration of gatifloxacin (100 mg/kg/day and 200 mg/kg/day) for 3 and 12 days led to marked elevation of GLP-1 levels, accompanied by significant decrease in insulin levels and increase in plasma glucose. Similar results were found in normal rats treated with 3-day gatifloxacin. Gatifloxacin-stimulated GLP-1 release was further confirmed in NCI-H716 cells, which was abolished by diazoxide, a K{sub ATP} channel opener. QT-PCR analysis showed that gatifloxacin also upregulated expression of proglucagon and prohormone convertase 3 mRNA. To clarify the contradiction on elevated GLP-1 without insulinotropic effect, effects of GLP-1 and gatifloxacin on insulin release were investigated using INS-1 cells. We found that short exposure (2 h) to GLP-1 stimulated insulin secretion and biosynthesis, whereas long exposure (24 h and 48 h) to high level of GLP-1 inhibited insulin secretion and biosynthesis. Moreover, we also confirmed gatifloxacin acutely stimulated insulin secretion while chronically inhibited insulin biosynthesis. All the results gave an inference that gatifloxacin stimulated over-secretion of GLP-1, in turn, high levels of GLP-1 and gatifloxacin synergistically impaired insulin release, worsening hyperglycemia. -- Highlights: ► Gatifloxacin induced hyperglycemia both in diabetic rats and normal rats. ► Gatifloxacin enhanced GLP-1 secretion but inhibited insulin secretion in rats. ► Long-term exposure to high GLP-1 inhibited insulin secretion and biosynthesis. ► GLP-1 over-secretion may be

  17. Effects of sleep restriction on glucose control and insulin secretion during diet-induced weight loss

    PubMed Central

    Nedeltcheva, A. V.; Imperial, J. G.; Penev, P. D.

    2012-01-01

    Insufficient sleep is associated with changes in glucose tolerance, insulin secretion, and insulin action. Despite widespread use of weight-loss diets for metabolic risk reduction, the effects of insufficient sleep on glucose regulation in overweight dieters are not known. To examine the consequences of recurrent sleep restriction on 24-hour blood glucose control during diet-induced weight loss, 10 overweight and obese adults (3F/7M; mean [SD] age 41 [5] y; BMI 27.4 [2.0] kg/m2) completed two 14-day treatments with hypocaloric diet and 8.5 or 5.5-h nighttime sleep opportunity in random order 7 [3] months apart. Oral and intravenous glucose tolerance test (IVGTT) data, fasting lipids and free-fatty acids (FFA), and 24-hour blood glucose, insulin, C-peptide, and counter-regulatory hormone measurements were collected after each treatment. Participants had comparable weight loss (1.0 [0.3] BMI units) during each treatment. Bedtime restriction reduced sleep by 131 [30] min/day. Recurrent sleep curtailment decreased 24-hour serum insulin concentrations (i.e. enhanced 24-hour insulin economy) without changes in oral glucose tolerance and 24-hour glucose control. This was accompanied by a decline in fasting blood glucose, increased fasting FFA which suppressed normally following glucose ingestion, and lower total and LDL cholesterol concentrations. Sleep-loss-related changes in counter-regulatory hormone secretion during the IVGTT limited the utility of the test in this study. In conclusion, sleep restriction enhanced 24-hour insulin economy without compromising glucose homeostasis in overweight individuals placed on a balanced hypocaloric diet. The changes in fasting blood glucose, insulin, lipid and FFA concentrations in sleep-restricted dieters resembled the pattern of human metabolic adaptation to reduced carbohydrate availability. PMID:22513492

  18. Theophylline prevents the inhibitory effect of prostaglandin E2 on glucose-induced insulin secretion in man.

    PubMed

    Giugliano, D; Cozzolino, D; Salvatore, T; Giunta, R; Torella, R

    1988-06-01

    This study was undertaken to assess the mechanism by which prostaglandins of the E series inhibit glucose-induced insulin secretion in man. Acute insulin response (mean change 3-10 min) to iv glucose (0.33 g/kg) was decreased by 40% during the infusion of prostaglandin E2 (10 micrograms/min) and glucose disappearance rates were reduced (P less than 0.05). Insulin response to arginine (5 g iv) and tolbutamide (1 g iv) were not affected by the same rate of prostaglandin E2 infusion. The inhibitory effect of prostaglandin E2 on glucose-induced insulin secretion was prevented by theophylline (100 mg as a loading dose followed by a 5 mg/min infusion), a drug that increases the intracellular cAMP concentrations by inhibiting phosphodiesterase activity. Our data suggest the involvement of the adenylate cyclase system in the inhibitory action of prostaglandin E2 on glucose-induced insulin secretion in man.

  19. Hormones and Obesity: Changes in Insulin and Growth Hormone Secretion Following Surgically Induced Weight Loss

    PubMed Central

    Crockford, P. M.; Salmon, P. A.

    1970-01-01

    Ten obese patients were subjected to insulin tolerance tests (0.2 unit per kg. regular insulin intravenously) and/or treadmill exercise tolerance testing (2.6 m.p.h. at 11° angulation) before and after surgically induced weight reduction. Immunoreactive growth hormone (IRGH) responses returned to normal with weight reduction in all but one—a grossly obese woman studied relatively early in the postoperative period when still far from the ideal body weight. Five of these patients and two additional subjects had intravenous glucose tolerance tests (0.5 g. per kg.) before and after weight reduction. In all, there was a significant diminution in immunoreactive insulin (IRI) values, accompained by little or no change in the glucose disappearance rate (KG) and a significant improvement in insulin effectiveness as indicated by the calculated “insulinogenic index”. It was concluded that the abnormalities in IRGH and IRI secretion, as well as the insulin resistance in obesity, are probably secondary and not of primary importance in the etiology of this disorder. PMID:5430052

  20. Rosuvastatin Treatment Affects Both Basal and Glucose-Induced Insulin Secretion in INS-1 832/13 Cells

    PubMed Central

    Salunkhe, Vishal A.; Elvstam, Olof; Eliasson, Lena; Wendt, Anna

    2016-01-01

    Rosuvastatin is a member of the statin family. Like the other statins it is prescribed to lower cholesterol levels and thereby reduce the risk of cardiovascular events. Rosuvastatin lowers the cholesterol levels by inhibiting the key enzyme 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-CoA reductase) in the cholesterol producing mevalonate pathway. It has been recognized that apart from their beneficial lipid lowering effects, statins also exhibit diabetogenic properties. The molecular mechanisms behind these remain unresolved. To investigate the effects of rosuvastatin on insulin secretion, we treated INS-1 832/13 cells with varying doses (20 nM to 20 μM) of rosuvastatin for 48 h. At concentrations of 2 μM and above basal insulin secretion was significantly increased. Using diazoxide we could determine that rosuvastatin did not increase basal insulin secretion by corrupting the KATP channels. Glucose-induced insulin secretion on the other hand seemed to be affected differently at different rosuvastatin concentrations. Rosuvastatin treatment (20 μM) for 24–48 h inhibited voltage-gated Ca2+ channels, which lead to reduced depolarization-induced exocytosis of insulin-containing granules. At lower concentrations of rosuvastatin (≤ 2 μM) the stimulus-secretion coupling pathway was intact downstream of the KATP channels as assessed by the patch clamp technique. However, a reduction in glucose-induced insulin secretion could be observed with rosuvastatin concentrations as low as 200 nM. The inhibitory effects of rosuvastatin on glucose-induced insulin secretion could be reversed with mevalonate, but not squalene, indicating that rosuvastatin affects insulin secretion through its effects on the mevalonate pathway, but not through the reduction of cholesterol biosynthesis. Taken together, these data suggest that rosuvastatin has the potential to increase basal insulin secretion and reduce glucose-induced insulin secretion. The latter is possibly an unavoidable

  1. Investigation of the mechanisms contributing to the compensatory increase in insulin secretion during dexamethasone-induced insulin resistance in rhesus macaques.

    PubMed

    Cummings, Bethany P; Bremer, Andrew A; Kieffer, Timothy J; D'Alessio, David; Havel, Peter J

    2013-02-01

    Dexamethasone has well-described effects to induce insulin resistance and increase insulin secretion. Herein, we examined potential contributors to the effect of dexamethasone to increase insulin secretion in rhesus macaques. Six male rhesus macaques received daily injections of either saline or dexamethasone (0.25 mg/kg i.m. for 7 days) in random order with 3 weeks between treatments. At the end of the treatment period, animals were fasted overnight and underwent a feeding study the next day, during which blood samples were taken before and for 60 min after a meal in order to assess islet hormone and incretin secretion. Dexamethasone induced marked increases in fasting plasma insulin, glucagon, leptin, and adiponectin concentrations (P<0.05). Surprisingly, the glycemic response after meal ingestion was decreased twofold during dexamethasone treatment (P<0.05). Dexamethasone-treated animals exhibited a significant increase in both insulin and glucose-dependent insulinotropic polypeptide (GIP) secretion during the feeding study (P<0.05). However, glucagon-like peptide-1 secretion was significantly lower in dexamethasone-treated animals compared with controls (P<0.01). Fasting and meal-stimulated pancreatic polypeptide concentrations (an index of the parasympathetic input to the islet) did not differ between saline and dexamethasone treatments. However, the proinsulin:insulin ratio was decreased throughout the feeding study with dexamethasone treatment suggesting an improvement of β-cell function (P<0.05). In conclusion, the maintenance of euglycemia and reduction of postprandial glycemia with short-term dexamethasone treatment appears to be due to the marked elevations of fasting and meal-stimulated insulin secretion. Furthermore, increases in postprandial GIP secretion with dexamethasone treatment appear to contribute to the effect of dexamethasone treatment to increase insulin secretion.

  2. Heat shock protein 72 protects insulin-secreting beta cells from lipopolysaccharide-induced endoplasmic reticulum stress.

    PubMed

    Hagiwara, Satoshi; Iwasaka, Hideo; Shingu, Chihiro; Matsumoto, Shigekiyo; Hasegawa, Akira; Asai, Nobuhiko; Noguchi, Takayuki

    2009-12-01

    Hyperthermia-induced activation of stress response proteins allows cells to withstand metabolic insults. In this study we set out to determine whether insulin secretion by pancreatic beta cells was affected by the acute inflammatory response, systemic inflammation-induced hyperglycaemia, and whole-body hyperthermia. Given that systemic-inflammation induces ER stress, we further examined whether hyperthermia can attenuate the extent of LPS-induced ER stress. Rats were randomised and divided into three treatment groups. Control rats received a 0.9% NaCl solution. Rats in the lipopolysaccharide (LPS) group received 7.5 mg of LPS/kg. Rats in the whole-body hyperthermia (WBH) + LPS group were exposed to 42 degrees C for 15 min, followed by injection with 7.5 mg of LPS/kg after 48 h. Glucose-potentiated insulin release and extent of ER stress were measured in beta cells. LPS inhibited glucose-induced insulin release from islet cells and induced the expression of Bip/GRP78, XBP-1, and CHOP transcripts. The inhibition of glucose-induced insulin release and induction of ER stress proteins by LPS was attenuated by WBH. Our findings suggest that LPS-induced systemic inflammation decreased insulin release due to the effects of ER stress proteins on insulin secretion. Furthermore, the induction of ER stress proteins was prevented by pretreating rats with WBH. This may suggest that inhibiting the induction of ER stress proteins through WBH can restore insulin release in various disease states.

  3. Host Genotype and Gut Microbiome Modulate Insulin Secretion and Diet-Induced Metabolic Phenotypes.

    PubMed

    Kreznar, Julia H; Keller, Mark P; Traeger, Lindsay L; Rabaglia, Mary E; Schueler, Kathryn L; Stapleton, Donald S; Zhao, Wen; Vivas, Eugenio I; Yandell, Brian S; Broman, Aimee Teo; Hagenbuch, Bruno; Attie, Alan D; Rey, Federico E

    2017-02-14

    Genetic variation drives phenotypic diversity and influences the predisposition to metabolic disease. Here, we characterize the metabolic phenotypes of eight genetically distinct inbred mouse strains in response to a high-fat/high-sucrose diet. We found significant variation in diabetes-related phenotypes and gut microbiota composition among the different mouse strains in response to the dietary challenge and identified taxa associated with these traits. Follow-up microbiota transplant experiments showed that altering the composition of the gut microbiota modifies strain-specific susceptibility to diet-induced metabolic disease. Animals harboring microbial communities with enhanced capacity for processing dietary sugars and for generating hydrophobic bile acids showed increased susceptibility to metabolic disease. Notably, differences in glucose-stimulated insulin secretion between different mouse strains were partially recapitulated via gut microbiota transfer. Our results suggest that the gut microbiome contributes to the genetic and phenotypic diversity observed among mouse strains and provide a link between the gut microbiome and insulin secretion.

  4. A genetically engineered human pancreatic β cell line exhibiting glucose-inducible insulin secretion.

    PubMed

    Ravassard, Philippe; Hazhouz, Yasmine; Pechberty, Séverine; Bricout-Neveu, Emilie; Armanet, Mathieu; Czernichow, Paul; Scharfmann, Raphael

    2011-09-01

    Despite intense efforts over the past 30 years, human pancreatic β cell lines have not been available. Here, we describe a robust technology for producing a functional human β cell line using targeted oncogenesis in human fetal tissue. Human fetal pancreatic buds were transduced with a lentiviral vector that expressed SV40LT under the control of the insulin promoter. The transduced buds were then grafted into SCID mice so that they could develop into mature pancreatic tissue. Upon differentiation, the newly formed SV40LT-expressing β cells proliferated and formed insulinomas. The resulting β cells were then transduced with human telomerase reverse transcriptase (hTERT), grafted into other SCID mice, and finally expanded in vitro to generate cell lines. One of these cell lines, EndoC-βH1, expressed many β cell-specific markers without any substantial expression of markers of other pancreatic cell types. The cells secreted insulin when stimulated by glucose or other insulin secretagogues, and cell transplantation reversed chemically induced diabetes in mice. These cells represent a unique tool for large-scale drug discovery and provide a preclinical model for cell replacement therapy in diabetes. This technology could be generalized to generate other human cell lines when the cell type-specific promoter is available.

  5. Resveratrol supplementation restores high-fat diet-induced insulin secretion dysfunction by increasing mitochondrial function in islet

    PubMed Central

    Kong, Wen; Zheng, Juan; Zhang, Hao-hao; Hu, Xiang; Zeng, Tian-shu; Hu, Di

    2015-01-01

    Resveratrol (RSV), a natural compound, is known for its effects on energy homeostasis. Here we investigated the effects of RSV and possible mechanism in insulin secretion of high-fat diet rats. Rats were randomly divided into three groups as follows: NC group (animals were fed ad libitum with normal chow for 8 weeks), HF group (animals were fed ad libitum with high-fat diet for 8 weeks), and HFR group (animals were treated with high-fat diet and administered with RSV for 8 weeks). Insulin secretion ability of rats was assessed by hyperglycemic clamp. Mitochondrial biogenesis genes, mitochondrial respiratory chain activities, reactive oxidative species (ROS), and several mitochondrial antioxidant enzyme activities were evaluated in islet. We found that HF group rats clearly showed low insulin secretion and mitochondrial complex dysfunction. Expression of silent mating type information regulation 2 homolog- 1 (SIRT1) and related mitochondrial biogenesis were significantly decreased. However, RSV administration group (HFR) showed a marked potentiation of glucose-stimulated insulin secretion. This effect was associated with elevated SIRT1 protein expression and antioxidant enzyme activities, resulting in increased mitochondrial respiratory chain activities and decreased ROS level. This study suggests that RSV may increase islet mitochondrial complex activities and antioxidant function to restore insulin secretion dysfunction induced by high-fat diet. PMID:25228148

  6. Resveratrol supplementation restores high-fat diet-induced insulin secretion dysfunction by increasing mitochondrial function in islet.

    PubMed

    Kong, Wen; Chen, Lu-lu; Zheng, Juan; Zhang, Hao-hao; Hu, Xiang; Zeng, Tian-shu; Hu, Di

    2015-02-01

    Resveratrol (RSV), a natural compound, is known for its effects on energy homeostasis. Here we investigated the effects of RSV and possible mechanism in insulin secretion of high-fat diet rats. Rats were randomly divided into three groups as follows: NC group (animals were fed ad libitum with normal chow for 8 weeks), HF group (animals were fed ad libitum with high-fat diet for 8 weeks), and HFR group (animals were treated with high-fat diet and administered with RSV for 8 weeks). Insulin secretion ability of rats was assessed by hyperglycemic clamp. Mitochondrial biogenesis genes, mitochondrial respiratory chain activities, reactive oxidative species (ROS), and several mitochondrial antioxidant enzyme activities were evaluated in islet. We found that HF group rats clearly showed low insulin secretion and mitochondrial complex dysfunction. Expression of silent mating type information regulation 2 homolog- 1 (SIRT1) and related mitochondrial biogenesis were significantly decreased. However, RSV administration group (HFR) showed a marked potentiation of glucose-stimulated insulin secretion. This effect was associated with elevated SIRT1 protein expression and antioxidant enzyme activities, resulting in increased mitochondrial respiratory chain activities and decreased ROS level. This study suggests that RSV may increase islet mitochondrial complex activities and antioxidant function to restore insulin secretion dysfunction induced by high-fat diet. © 2014 by the Society for Experimental Biology and Medicine.

  7. Chronic effects of palmitate overload on nutrient-induced insulin secretion and autocrine signalling in pancreatic MIN6 beta cells.

    PubMed

    Watson, Maria L; Macrae, Katherine; Marley, Anna E; Hundal, Harinder S

    2011-01-01

    Sustained exposure of pancreatic β cells to an increase in saturated fatty acids induces pleiotropic effects on β-cell function, including a reduction in stimulus-induced insulin secretion. The objective of this study was to investigate the effects of chronic over supply of palmitate upon glucose- and amino acid-stimulated insulin secretion (GSIS and AASIS, respectively) and autocrine-dependent insulin signalling with particular focus on the importance of ceramide, ERK and CaMKII signalling. GSIS and AASIS were both stimulated by >7-fold resulting in autocrine-dependent activation of protein kinase B (PKB, also known as Akt). Insulin release was dependent upon nutrient-induced activation of calcium/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) as their pharmacological inhibition suppressed GSIS/AASIS significantly. Chronic (48 h, 0.4 mM) palmitate treatment blunted glucose/AA-induced activation of CaMKII and ERK and caused a concomitant reduction (~75%) in GSIS/AASIS and autocrine-dependent activation of PKB. This inhibition could not be attributed to enhanced mitochondrial fatty acid uptake/oxidation or ceramide synthesis, which were unaffected by palmitate. In contrast, diacylglycerol synthesis was elevated suggesting increased palmitate esterification rather than oxidation may contribute to impaired stimulus-secretion coupling. Consistent with this, 2-bromopalmitate, a non-oxidisable palmitate analogue, inhibited GSIS as effectively as palmitate. Our results exclude changes in ceramide content or mitochondrial fatty acid handling as factors initiating palmitate-induced defects in insulin release from MIN6 β cells, but suggest that reduced CaMKII and ERK activation associated with palmitate overload may contribute to impaired stimulus-induced insulin secretion.

  8. Chronic Effects of Palmitate Overload on Nutrient-Induced Insulin Secretion and Autocrine Signalling in Pancreatic MIN6 Beta Cells

    PubMed Central

    Watson, Maria L.; Macrae, Katherine; Marley, Anna E.; Hundal, Harinder S.

    2011-01-01

    Background Sustained exposure of pancreatic β cells to an increase in saturated fatty acids induces pleiotropic effects on β-cell function, including a reduction in stimulus-induced insulin secretion. The objective of this study was to investigate the effects of chronic over supply of palmitate upon glucose- and amino acid-stimulated insulin secretion (GSIS and AASIS, respectively) and autocrine-dependent insulin signalling with particular focus on the importance of ceramide, ERK and CaMKII signalling. Principal Findings GSIS and AASIS were both stimulated by >7-fold resulting in autocrine-dependent activation of protein kinase B (PKB, also known as Akt). Insulin release was dependent upon nutrient-induced activation of calcium/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) as their pharmacological inhibition suppressed GSIS/AASIS significantly. Chronic (48 h, 0.4 mM) palmitate treatment blunted glucose/AA-induced activation of CaMKII and ERK and caused a concomitant reduction (∼75%) in GSIS/AASIS and autocrine-dependent activation of PKB. This inhibition could not be attributed to enhanced mitochondrial fatty acid uptake/oxidation or ceramide synthesis, which were unaffected by palmitate. In contrast, diacylglycerol synthesis was elevated suggesting increased palmitate esterification rather than oxidation may contribute to impaired stimulus-secretion coupling. Consistent with this, 2-bromopalmitate, a non-oxidisable palmitate analogue, inhibited GSIS as effectively as palmitate. Conclusions Our results exclude changes in ceramide content or mitochondrial fatty acid handling as factors initiating palmitate-induced defects in insulin release from MIN6 β cells, but suggest that reduced CaMKII and ERK activation associated with palmitate overload may contribute to impaired stimulus-induced insulin secretion. PMID:21998735

  9. Evidence for the involvement of GPR40 and NADPH oxidase in palmitic acid-induced superoxide production and insulin secretion.

    PubMed

    Graciano, Maria Fernanda; Valle, Maíra Mello; Curi, Rui; Carpinelli, Angelo Rafael

    2013-01-01

    G protein coupled receptor 40 (GPR40) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex have been shown to be involved in the fatty acid amplification of glucose-stimulated insulin secretion (GSIS). The effect of palmitic acid on superoxide production and insulin secretion by INS-1E cells and the possible involvement of GPR40 and NADPH oxidase in these processes were examined in this study. Cells were incubated during 1 h with palmitic acid in low and high glucose concentrations, a GPR40 agonist (GW9508) and inhibitors of NADPH oxidase (diphenyleneiodonium, DPI) and PKC (calphostin C). GW9508 induced superoxide production at 2.8 and 5.6 mM glucose concentrations and stimulated insulin secretion at 16.7 mM glucose concentration involving both PKC and NADPH oxidase activation. Palmitic acid induced superoxide production through NADPH oxidase and GPR40-dependent pathways and the stimulation of insulin secretion in the presence of a high glucose concentration was reduced by knockdown of GPR40 using siRNA. Our results suggest that palmitic acid induces superoxide production and potentiates GSIS through NADPH oxidase and GPR40 pathways in pancreatic ? cells.

  10. Long-term high animal protein diet reduces body weight gain and insulin secretion in diet-induced obese rats.

    PubMed

    Chen, Haiyan; Wang, Yiling; Ma, Lichuan; Zhao, Jiajun; Li, Yinyin; Li, Minglong

    2012-10-01

    The effects of a high protein diet on insulin secretion and glucose metabolism have been quite controversial. The aim of this study was to evaluate the effects of long-term isocaloric high animal protein intake on insulin secretion in diet-induced obese rats. After the experimental period (24 weeks), the high-fat diet-induced obese rats that were fed isocaloric high-protein diets (HP) had lower body weight gain (P < 0.01) and lower visceral fat (P < 0.05) than normal protein (NP) rats. Fasting plasma glucagon-like peptide-1 (GLP-1) was also reduced significantly (P < 0.05), as well as serum insulin levels at 5 min and 10 min by intravenous insulin releasing test. In addition, insulin mRNA and pancreatic duodenal homeodomain-1 (PDX-1), GLP-1 protein expression were both markedly lower in HP rats (P < 0.05), while PDX-1 mRNA in HP rats had no difference from NP rats. These results suggest that long-term isocaloric high animal protein intake reduces the acute insulin response in obese rats and the decrease of insulin is associated with both reduced weight gain and inhibition of PDX-1 expression. GLP-1 might be a negative feedback for the balance of energy metabolism secondary to changes of body weight and visceral fat. Copyright © 2012 Society of Chemical Industry.

  11. Relaxation response induces temporal transcriptome changes in energy metabolism, insulin secretion and inflammatory pathways.

    PubMed

    Bhasin, Manoj K; Dusek, Jeffery A; Chang, Bei-Hung; Joseph, Marie G; Denninger, John W; Fricchione, Gregory L; Benson, Herbert; Libermann, Towia A

    2013-01-01

    The relaxation response (RR) is the counterpart of the stress response. Millennia-old practices evoking the RR include meditation, yoga and repetitive prayer. Although RR elicitation is an effective therapeutic intervention that counteracts the adverse clinical effects of stress in disorders including hypertension, anxiety, insomnia and aging, the underlying molecular mechanisms that explain these clinical benefits remain undetermined. To assess rapid time-dependent (temporal) genomic changes during one session of RR practice among healthy practitioners with years of RR practice and also in novices before and after 8 weeks of RR training, we measured the transcriptome in peripheral blood prior to, immediately after, and 15 minutes after listening to an RR-eliciting or a health education CD. Both short-term and long-term practitioners evoked significant temporal gene expression changes with greater significance in the latter as compared to novices. RR practice enhanced expression of genes associated with energy metabolism, mitochondrial function, insulin secretion and telomere maintenance, and reduced expression of genes linked to inflammatory response and stress-related pathways. Interactive network analyses of RR-affected pathways identified mitochondrial ATP synthase and insulin (INS) as top upregulated critical molecules (focus hubs) and NF-κB pathway genes as top downregulated focus hubs. Our results for the first time indicate that RR elicitation, particularly after long-term practice, may evoke its downstream health benefits by improving mitochondrial energy production and utilization and thus promoting mitochondrial resiliency through upregulation of ATPase and insulin function. Mitochondrial resiliency might also be promoted by RR-induced downregulation of NF-κB-associated upstream and downstream targets that mitigates stress.

  12. Relaxation Response Induces Temporal Transcriptome Changes in Energy Metabolism, Insulin Secretion and Inflammatory Pathways

    PubMed Central

    Joseph, Marie G.; Denninger, John W.; Fricchione, Gregory L.; Benson, Herbert; Libermann, Towia A.

    2013-01-01

    The relaxation response (RR) is the counterpart of the stress response. Millennia-old practices evoking the RR include meditation, yoga and repetitive prayer. Although RR elicitation is an effective therapeutic intervention that counteracts the adverse clinical effects of stress in disorders including hypertension, anxiety, insomnia and aging, the underlying molecular mechanisms that explain these clinical benefits remain undetermined. To assess rapid time-dependent (temporal) genomic changes during one session of RR practice among healthy practitioners with years of RR practice and also in novices before and after 8 weeks of RR training, we measured the transcriptome in peripheral blood prior to, immediately after, and 15 minutes after listening to an RR-eliciting or a health education CD. Both short-term and long-term practitioners evoked significant temporal gene expression changes with greater significance in the latter as compared to novices. RR practice enhanced expression of genes associated with energy metabolism, mitochondrial function, insulin secretion and telomere maintenance, and reduced expression of genes linked to inflammatory response and stress-related pathways. Interactive network analyses of RR-affected pathways identified mitochondrial ATP synthase and insulin (INS) as top upregulated critical molecules (focus hubs) and NF-κB pathway genes as top downregulated focus hubs. Our results for the first time indicate that RR elicitation, particularly after long-term practice, may evoke its downstream health benefits by improving mitochondrial energy production and utilization and thus promoting mitochondrial resiliency through upregulation of ATPase and insulin function. Mitochondrial resiliency might also be promoted by RR-induced downregulation of NF-κB-associated upstream and downstream targets that mitigates stress. PMID:23650531

  13. Role of alpha 1- and alpha 2-adrenoceptors in catecholamine-induced hyperglycaemia, lipolysis and insulin secretion in conscious fasted rabbits.

    PubMed

    Moratinos, J; Carpene, C; de Pablos, I; Reverte, M

    1988-06-01

    1. In conscious fasted rabbits an intravenous infusion of clonidine (2 micrograms kg-1 min-1) induced hyperglycaemia. The increase in blood glucose was accompanied by an inhibition of insulin secretion and basal lipolysis. 2. Yohimbine infused at a rate of 20 micrograms kg-1 min-1 suppressed clonidine-induced hyperglycaemia and blocked the inhibitory effect on insulin secretion mediated by the alpha 2-adrenoceptor agonist. 3. The intravenous infusion of amidephrine (10 micrograms kg-1 min-1) induced an increase in insulin secretion in the absence of patent hyperglycaemia. Prazosin, 0.3 mg kg-1 s.c. selectively antagonized the effect of amidephrine on insulin secretion. 4. Isoprenaline infusion (4.4 micrograms kg-1 min-1) evoked a significant increase in blood glycerol and immunoreactive insulin plasma levels. Both responses were clearly attenuated when alpha 2-adrenoceptors were simultaneously stimulated by selective (clonidine) and less selective (phenylephrine, 20 micrograms kg-1 min-1) agonists. 5. Amidephrine infusion did not induce appreciable changes in blood glycerol nor did it modify, isoprenaline-induced lipolytic response. 6. Simultaneous infusion of isoprenaline and amidephrine induced a remarkable increase in insulin secretion. 7. It is concluded that in normal fasted rabbits stimulation of alpha 2-adrenoceptors depresses basal and beta-adrenoceptor mediated lipolysis and insulin secretion. On the other hand, selective stimulation of alpha 1-adrenoceptors does not affect lipolysis but induces insulin release. Simultaneous stimulation of alpha 1- and beta-adrenoceptors potentiates the insulin secretory response.

  14. L-cysteine reversibly inhibits glucose-induced biphasic insulin secretion and ATP production by inactivating PKM2.

    PubMed

    Nakatsu, Daiki; Horiuchi, Yuta; Kano, Fumi; Noguchi, Yoshiyuki; Sugawara, Taichi; Takamoto, Iseki; Kubota, Naoto; Kadowaki, Takashi; Murata, Masayuki

    2015-03-10

    Increase in the concentration of plasma L-cysteine is closely associated with defective insulin secretion from pancreatic β-cells, which results in type 2 diabetes (T2D). In this study, we investigated the effects of prolonged L-cysteine treatment on glucose-stimulated insulin secretion (GSIS) from mouse insulinoma 6 (MIN6) cells and from mouse pancreatic islets, and found that the treatment reversibly inhibited glucose-induced ATP production and resulting GSIS without affecting proinsulin and insulin synthesis. Comprehensive metabolic analyses using capillary electrophoresis time-of-flight mass spectrometry showed that prolonged L-cysteine treatment decreased the levels of pyruvate and its downstream metabolites. In addition, methyl pyruvate, a membrane-permeable form of pyruvate, rescued L-cysteine-induced inhibition of GSIS. Based on these results, we found that both in vitro and in MIN6 cells, L-cysteine specifically inhibited the activity of pyruvate kinase muscle isoform 2 (PKM2), an isoform of pyruvate kinases that catalyze the conversion of phosphoenolpyruvate to pyruvate. L-cysteine also induced PKM2 subunit dissociation (tetramers to dimers/monomers) in cells, which resulted in impaired glucose-induced ATP production for GSIS. DASA-10 (NCGC00181061, a substituted N,N'-diarylsulfonamide), a specific activator for PKM2, restored the tetramer formation and the activity of PKM2, glucose-induced ATP production, and biphasic insulin secretion in L-cysteine-treated cells. Collectively, our results demonstrate that impaired insulin secretion due to exposure to L-cysteine resulted from its direct binding and inactivation of PKM2 and suggest that PKM2 is a potential therapeutic target for T2D.

  15. Oscillatory control of insulin secretion.

    PubMed

    Tengholm, Anders; Gylfe, Erik

    2009-01-15

    Pancreatic beta-cells possess an inherent ability to generate oscillatory signals that trigger insulin release. Coordination of the secretory activity among beta-cells results in pulsatile insulin secretion from the pancreas, which is considered important for the action of the hormone in the target tissues. This review focuses on the mechanisms underlying oscillatory control of insulin secretion at the level of the individual beta-cell. Recent studies have demonstrated that oscillations of the cytoplasmic Ca(2+) concentration are synchronized with oscillations in beta-cell metabolism, intracellular cAMP concentration, phospholipase C activity and plasma membrane phosphoinositide lipid concentrations. There are complex interdependencies between the different messengers and signalling pathways that contribute to amplitude regulation and shaping of the insulin secretory response to nutrient stimuli and neurohormonal modulators. Several of these pathways may be important pharmacological targets for improving pulsatile insulin secretion in type 2 diabetes.

  16. Glucose-induced electrical activities and insulin secretion in pancreatic islet β-cells are modulated by CFTR

    PubMed Central

    Guo, Jing Hui; Chen, Hui; Ruan, Ye Chun; Zhang, Xue Lian; Zhang, Xiao Hu; Fok, Kin Lam; Tsang, Lai Ling; Yu, Mei Kuen; Huang, Wen Qing; Sun, Xiao; Chung, Yiu Wa; Jiang, Xiaohua; Sohma, Yoshiro; Chan, Hsiao Chang

    2014-01-01

    The cause of insulin insufficiency remains unknown in many diabetic cases. Up to 50% adult patients with cystic fibrosis (CF), a disease caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR), develop CF-related diabetes (CFRD) with most patients exhibiting insulin insufficiency. Here we show that CFTR is a regulator of glucose-dependent electrical acitivities and insulin secretion in β-cells. We demonstrate that glucose elicited whole-cell currents, membrane depolarization, electrical bursts or action potentials, Ca2+ oscillations and insulin secretion are abolished or reduced by inhibitors or knockdown of CFTR in primary mouse β-cells or RINm5F β-cell line, or significantly attenuated in CFTR mutant (DF508) mice compared with wild-type mice. VX-809, a newly discovered corrector of DF508 mutation, successfully rescues the defects in DF508 β-cells. Our results reveal a role of CFTR in glucose-induced electrical activities and insulin secretion in β-cells, shed light on the pathogenesis of CFRD and possibly other idiopathic diabetes, and present a potential treatment strategy. PMID:25025956

  17. Leucine regulation of glucokinase and ATP synthase sensitizes glucose-induced insulin secretion in pancreatic beta-cells.

    PubMed

    Yang, Jichun; Wong, Ryan K; Park, MieJung; Wu, Jianmei; Cook, Joshua R; York, David A; Deng, Shaoping; Markmann, James; Naji, Ali; Wolf, Bryan A; Gao, Zhiyong

    2006-01-01

    We have recently shown that leucine culture upregulates ATP synthase beta-subunit (ATPSbeta) and increases ATP level, cytosolic Ca(2+), and glucose-induced insulin secretion in rat islets. The aim is to test whether glucokinase expression is also affected in rat islets and its role in glucose sensitization during leucine culture. Leucine culture increased glucose-induced NAD(P)H level at 1 and 2 days but not at 1 week. The half-maximal effective concentration of the glucose response curve for NAD(P)H was left-shifted from 5-7 to 2-3 mmol/l. The effect was dose dependent and rapamycin insensitive. Leucine culture did not affect glyceraldehyde effects on NAD(P)H. Leucine pretreatment for 30 min had no effects on NAD(P)H levels. Leucine culture for 2 days also increased glucose-induced cytosolic Ca(2+) elevation, ATP level, and insulin secretion. Leucine increase of glucokinase mRNA levels occurred as early as day 1 and lasted through 1 week. That of ATPSbeta did not occur until day 2 and lasted through 1 week. Leucine effects on both mRNAs were dose dependent. The upregulation of both genes was confirmed by Western blotting. Leucine culture also increased glucose-induced insulin secretion, ATP level, glucokinase, and ATPSbeta levels of type 2 diabetic human islets. In conclusion, leucine culture upregulates glucokinase, which increases NAD(P)H level, and ATPSbeta, which increases oxidation of NADH and production of ATP. The combined upregulation of both genes increases glucose-induced cytosolic Ca(2+) and insulin secretion.

  18. Mitochondrial oxidative stress mediates high-phosphate-induced secretory defects and apoptosis in insulin-secreting cells.

    PubMed

    Nguyen, Tuyet Thi; Quan, Xianglan; Hwang, Kyu-Hee; Xu, Shanhua; Das, Ranjan; Choi, Seong-Kyung; Wiederkehr, Andreas; Wollheim, Claes B; Cha, Seung-Kuy; Park, Kyu-Sang

    2015-06-01

    Inorganic phosphate (Pi) plays an important role in cell signaling and energy metabolism. In insulin-releasing cells, Pi transport into mitochondria is essential for the generation of ATP, a signaling factor in metabolism-secretion coupling. Elevated Pi concentrations, however, can have toxic effects in various cell types. The underlying molecular mechanisms are poorly understood. Here, we have investigated the effect of Pi on secretory function and apoptosis in INS-1E clonal β-cells and rat pancreatic islets. Elevated extracellular Pi (1~5 mM) increased the mitochondrial membrane potential (ΔΨm), superoxide generation, caspase activation, and cell death. Depolarization of the ΔΨm abolished Pi-induced superoxide generation. Butylmalonate, a nonselective blocker of mitochondrial phosphate transporters, prevented ΔΨm hyperpolarization, superoxide generation, and cytotoxicity caused by Pi. High Pi also promoted the opening of the mitochondrial permeability transition (PT) pore, leading to apoptosis, which was also prevented by butylmalonate. The mitochondrial antioxidants mitoTEMPO or MnTBAP prevented Pi-triggered PT pore opening and cytotoxicity. Elevated extracellular Pi diminished ATP synthesis, cytosolic Ca(2+) oscillations, and insulin content and secretion in INS-1E cells as well as in dispersed islet cells. These parameters were restored following preincubation with mitochondrial antioxidants. This treatment also prevented high-Pi-induced phosphorylation of ER stress proteins. We propose that elevated extracellular Pi causes mitochondrial oxidative stress linked to mitochondrial hyperpolarization. Such stress results in reduced insulin content and defective insulin secretion and cytotoxicity. Our data explain the decreased insulin content and secretion observed under hyperphosphatemic states.

  19. Thioredoxin-mimetic peptides (TXM) reverse auranofin induced apoptosis and restore insulin secretion in insulinoma cells.

    PubMed

    Cohen-Kutner, Moshe; Khomsky, Lena; Trus, Michael; Aisner, Yonatan; Niv, Masha Y; Benhar, Moran; Atlas, Daphne

    2013-04-01

    The thioredoxin reductase/thioredoxin system (TrxR/Trx1) plays a major role in protecting cells from oxidative stress. Disruption of the TrxR-Trx1 system keeps Trx1 in the oxidized state leading to cell death through activation of the ASK1-Trx1 apoptotic pathway. The potential mechanism and ability of tri- and tetra-oligopeptides derived from the canonical -CxxC- motif of the Trx1-active site to mimic and enhance Trx1 cellular activity was examined. The Trx mimetics peptides (TXM) protected insulinoma INS 832/13 cells from oxidative stress induced by selectively inhibiting TrxR with auranofin (AuF). TXM reversed the AuF-effects preventing apoptosis, and increasing cell-viability. The TXM peptides were effective in inhibiting AuF-induced MAPK, JNK and p38(MAPK) phosphorylation, in correlation with preventing caspase-3 cleavage and thereby PARP-1 dissociation. The ability to form a disulfide-bridge-like conformation was estimated from molecular dynamics simulations. The TXM peptides restored insulin secretion and displayed Trx1 denitrosylase activity. Their potency was 10-100-fold higher than redox reagents like NAC, AD4, or ascorbic acid. Unable to reverse ERK1/2 phosphorylation, TXM-CB3 (NAc-Cys-Pro-Cys amide) appeared to function in part, through inhibiting ASK1-Trx dissociation. These highly effective anti-apoptotic effects of Trx1 mimetic peptides exhibited in INS 832/13 cells could become valuable in treating adverse oxidative-stress related disorders such as diabetes. Copyright © 2013 Elsevier Inc. All rights reserved.

  20. CCR2 knockout exacerbates cerulein-induced chronic pancreatitis with hyperglycemia via decreased GLP-1 receptor expression and insulin secretion.

    PubMed

    Nakamura, Yuji; Kanai, Takanori; Saeki, Keita; Takabe, Miho; Irie, Junichiro; Miyoshi, Jun; Mikami, Yohei; Teratani, Toshiaki; Suzuki, Takahiro; Miyata, Naoteru; Hisamatsu, Tadakazu; Nakamoto, Nobuhiro; Yamagishi, Yoshiyuki; Higuchi, Hajime; Ebinuma, Hirotoshi; Hozawa, Shigenari; Saito, Hidetsugu; Itoh, Hiroshi; Hibi, Toshifumi

    2013-04-15

    Glucagon-like peptide-1 (GLP-1) promotes insulin release; however, the relationship between the GLP-1 signal and chronic pancreatitis is not well understood. Here we focus on chemokine (C-C motif) ligand 2 (CCL2) and its receptor (CCR2) axis, which regulates various immune cells, including macrophages, to clarify the mechanism of GLP-1-mediated insulin secretion in chronic pancreatitis in mice. One and multiple series of repetitive cerulein administrations were used to induce acute and chronic cerulein pancreatitis, respectively. Acute cerulein-administered CCR2-knockout (KO) mice showed suppressed infiltration of CD11b(+)Gr-1(low) macrophages and pancreatic inflammation and significantly upregulated insulin secretion compared with paired wild-type (WT) mice. However, chronic cerulein-administered CCR2-KO mice showed significantly increased infiltration of CD11b(+)/Gr-1(-) and CD11b(+)/Gr-1(high) cells, but not CD11b(+)/Gr-1(low) cells, in pancreas with severe inflammation and significantly decreased insulin secretion compared with their WT counterparts. Furthermore, although serum GLP-1 levels in chronic cerulein-administered WT and CCR2-KO mice were comparably upregulated after cerulein administrations, GLP-1 receptor levels in pancreases of chronic cerulein-administered CCR2-KO mice were significantly lower than in paired WT mice. Nevertheless, a significantly higher hyperglycemia level in chronic cerulein-administered CCR2-KO mice was markedly restored by treatment with a GLP-1 analog to a level comparable to the paired WT mice. Collectively, the CCR2/CCL2 axis-mediated CD11b(+)-cell migration to the pancreas is critically involved in chronic pancreatitis-mediated hyperglycemia through the modulation of GLP-1 receptor expression and insulin secretion.

  1. Impairment of glucose-induced insulin secretion in human pancreatic islets transplanted to diabetic nude mice.

    PubMed

    Jansson, L; Eizirik, D L; Pipeleers, D G; Borg, L A; Hellerström, C; Andersson, A

    1995-08-01

    Hyperglycemia-induced beta-cell dysfunction may be an important component in the pathogenesis of non-insulin-dependent diabetes mellitus. However, most available data in this field were obtained from rodent islets. To investigate the relevance of this hypothesis for human beta-cells in vivo, human pancreatic islets were transplanted under the renal capsule of nude mice. Experimental groups were chosen so that grafted islets were exposed to either hyper- or normoglycemia or combinations of these for 4 or 6 wk. Grafts of normoglycemic recipients responded with an increased insulin release to a glucose stimulus during perfusion, whereas grafts of hyperglycemic recipients failed to respond to glucose. The insulin content of the grafts in the latter groups was only 10% of those observed in controls. Recipients initially hyperglycemic (4 wk), followed by 2 wk of normoglycemia regained a normal graft insulin content, but a decreased insulin response to glucose remained. No ultrastructural signs of beta-cell damage were observed, with the exception of increased glycogen deposits in animals hyperglycemic at the time of killing. It is concluded that prolonged exposure to a diabetic environment induces a long-term secretory defect in human beta-cells, which is not dependent on the size of the islet insulin stores.

  2. Impairment of glucose-induced insulin secretion in human pancreatic islets transplanted to diabetic nude mice.

    PubMed Central

    Jansson, L; Eizirik, D L; Pipeleers, D G; Borg, L A; Hellerström, C; Andersson, A

    1995-01-01

    Hyperglycemia-induced beta-cell dysfunction may be an important component in the pathogenesis of non-insulin-dependent diabetes mellitus. However, most available data in this field were obtained from rodent islets. To investigate the relevance of this hypothesis for human beta-cells in vivo, human pancreatic islets were transplanted under the renal capsule of nude mice. Experimental groups were chosen so that grafted islets were exposed to either hyper- or normoglycemia or combinations of these for 4 or 6 wk. Grafts of normoglycemic recipients responded with an increased insulin release to a glucose stimulus during perfusion, whereas grafts of hyperglycemic recipients failed to respond to glucose. The insulin content of the grafts in the latter groups was only 10% of those observed in controls. Recipients initially hyperglycemic (4 wk), followed by 2 wk of normoglycemia regained a normal graft insulin content, but a decreased insulin response to glucose remained. No ultrastructural signs of beta-cell damage were observed, with the exception of increased glycogen deposits in animals hyperglycemic at the time of killing. It is concluded that prolonged exposure to a diabetic environment induces a long-term secretory defect in human beta-cells, which is not dependent on the size of the islet insulin stores. Images PMID:7635965

  3. PED/PEA-15 regulates glucose-induced insulin secretion by restraining potassium channel expression in pancreatic beta-cells.

    PubMed

    Miele, Claudia; Raciti, Gregory Alexander; Cassese, Angela; Romano, Chiara; Giacco, Ferdinando; Oriente, Francesco; Paturzo, Flora; Andreozzi, Francesco; Zabatta, Assunta; Troncone, Giancarlo; Bosch, Fatima; Pujol, Anna; Chneiweiss, Hervé; Formisano, Pietro; Beguinot, Francesco

    2007-03-01

    The phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes (ped/pea-15) gene is overexpressed in human diabetes and causes this abnormality in mice. Transgenic mice with beta-cell-specific overexpression of ped/pea-15 (beta-tg) exhibited decreased glucose tolerance but were not insulin resistant. However, they showed impaired insulin response to hyperglycemia. Islets from the beta-tg also exhibited little response to glucose. mRNAs encoding the Sur1 and Kir6.2 potassium channel subunits and their upstream regulator Foxa2 were specifically reduced in these islets. Overexpression of PED/PEA-15 inhibited the induction of the atypical protein kinase C (PKC)-zeta by glucose in mouse islets and in beta-cells of the MIN-6 and INS-1 lines. Rescue of PKC-zeta activity elicited recovery of the expression of the Sur1, Kir6.2, and Foxa2 genes and of glucose-induced insulin secretion in PED/PEA-15-overexpressing beta-cells. Islets from ped/pea-15-null mice exhibited a twofold increased activation of PKC-zeta by glucose; increased abundance of the Sur1, Kir6.2, and Foxa2 mRNAs; and enhanced glucose effect on insulin secretion. In conclusion, PED/PEA-15 is an endogenous regulator of glucose-induced insulin secretion, which restrains potassium channel expression in pancreatic beta-cells. Overexpression of PED/PEA-15 dysregulates beta-cell function and is sufficient to impair glucose tolerance in mice.

  4. Evaluation of insulin sensitivity and secretion in primary aldosteronism.

    PubMed

    Watanabe, Daisuke; Yatabe, Midori; Ichihara, Atsuhiro

    In primary aldosteronism (PA), insulin response to glucose is not fully understood. Insulin action was elucidated using indices in 32 PA and 21 essential hypertension (EH) patients. These patients were evaluated using homeostasis model assessment (HOMA) indices, quantitative insulin sensitivity check index (QUICKI), and insulinogenic index (IGI), which were expressed for insulin sensitivity/secretion and the early phase of insulin secretion. Insulin sensitivity and early phase of insulin secretion were decreased in PA, and there was a negative correlation between serum potassium concentration and insulin sensitivity indices. These findings suggest that glucose intolerance in PA may be caused by hypokalemia-induced insulin resistance and hypokalemia-independent impairment of early-phase insulin secretion.

  5. PAX4 promotes PDX1-induced differentiation of mesenchymal stem cells into insulin-secreting cells

    PubMed Central

    Xu, Lifa; Xu, Congjing; Zhou, Shuping; Liu, Xueke; Wang, Jian; Liu, Xinkuang; Qian, Suping; Xin, Yingru; Gao, Yi; Zhu, Yongqiang; Tang, Xiaolong

    2017-01-01

    A shortage of postmortem pancreatic tissue for islet isolation impedes the application of cell replacement therapy in patients with diabetes. As an alternative for islet cell transplantation, transcription factors, including PDX1, PAX4, and neurogenin-3, that aid in the formation of insulin-producing β cells during development have been investigated. The present study evaluated the effects of PAX4 and PDX1 on the differentiation of mesenchymal stem cells (MSCs) into insulin-producing β-like cells in vitro using recombinant adenoviruses carrying PDX1 or PDX1 plus PAX4. RT-PCR, Western blot, and immunofluorescence assays were used to detect the expression levels of relevant genes and proteins, and enzyme-linked immunosorbent assays were used to determine the amount of insulin and C-peptide secreted by the virus-infected cells following stimulation with high glucose. The results showed that PAX4 markedly enhanced the propensity of PDX1-positive MSCs to form mature islet-like clusters and functional insulin-producing β-like cells. Our findings provide a novel foundation for generating β-like cells from MSCs with PAX4 and PDX1 for future clinical application. PMID:28386318

  6. Ghrelin, a natural GH secretagogue produced by the stomach, induces hyperglycemia and reduces insulin secretion in humans.

    PubMed

    Broglio, F; Arvat, E; Benso, A; Gottero, C; Muccioli, G; Papotti, M; van der Lely, A J; Deghenghi, R; Ghigo, E

    2001-10-01

    Ghrelin, a 28 amino acid gastric hormone is a natural ligand of the GH Secretagogue (GHS) receptor (GHS-R) and strongly stimulates GH secretion though, like synthetic GHS, it shows other endocrine and non-endocrine activities. Aim of the present study was to clarify whether ghrelin administration influences insulin and glucose levels in humans. To this goal, we compared the effects of ghrelin, hexarelin, a synthetic GHS, or placebo on insulin and glucose as well as on GH levels in 11 normal young volunteers (age [mean +/- SEM]: 28.5 +/- 3.1 yr; BMI: 22.2 +/- 0.9 Kg/m(2)). Ghrelin induced very marked increase in GH secretion (DeltaAUC(0-180): 5777.1 +/- 812.6 microg/l/h; p < 0.01) which was not modified by placebo. Placebo administration did not modify insulin and glucose levels. On the other hand, ghrelin administration induced a prompt increase in glucose levels (DeltaAUC(0-180): 1343.1 +/- 443.5 mg/dl/h; p < 0.01 vs. saline). Absolute glucose levels at +15' were already higher than those at baseline (93.9 +/- 7.1 mg/dl; p < 0.01) and persisted elevated up to 165' (90.3 +/- 5.8 mg/dl; p < 0.01 vs. 0'). Ghrelin administration was also followed by a decrease in serum insulin levels (DeltaAUC(0-180): -207.1 +/- 70.5 mU/l/h; p < 0.05 vs. saline). Absolute insulin levels were significantly reduced from 30' (11.4 +/- 0.9 mU/l, p < 0.1 vs. 0'), showed the nadir at +45' (10.0 +/- 0.6 mU/l, p < 0.01 vs. 0') and then persisted lower (p < 0.01) than baseline up to +105'. Hexarelin administration did not modify glucose and insulin levels despite its marked GH-releasing effect (DeltaAUC(0-180): 4156.8 +/- 1180.3 microg/l/h; p < 0.01 vs. saline) that was slightly lower (p < 0.05) than that of ghrelin. In conclusion, these findings show that, besides stimulating GH secretion, ghrelin is a gastric hormone possessing metabolic actions such as hyperglycemic effect and lowering effect on insulin secretion in humans, at least after acute administration.

  7. ERAD-icating mutant insulin promotes functional insulin secretion.

    PubMed

    Moore, Daniel J

    2017-01-18

    Overexpression of a chaperone protein liberates functional insulin from a misfolded mutant partner to improve insulin secretion. Copyright © 2017, American Association for the Advancement of Science.

  8. Nε-(carboxymethyl) lysine-induced mitochondrial fission and mitophagy cause decreased insulin secretion from β-cells.

    PubMed

    Lo, Mei-Chen; Chen, Ming-Hong; Lee, Wen-Sen; Lu, Chin-I; Chang, Chuang-Rung; Kao, Shu-Huei; Lee, Horng-Mo

    2015-11-15

    Nε-(carboxymethyl) lysine-conjugated bovine serum albumin (CML-BSA) is a major component of advanced glycation end products (AGEs). We hypothesised that AGEs reduce insulin secretion from pancreatic β-cells by damaging mitochondrial functions and inducing mitophagy. Mitochondrial morphology and the occurrence of autophagy were examined in pancreatic islets of diabetic db/db mice and in the cultured CML-BSA-treated insulinoma cell line RIN-m5F. In addition, the effects of α-lipoic acid (ALA) on mitochondria in AGE-damaged tissues were evaluated. The diabetic db/db mouse exhibited an increase in the number of autophagosomes in damaged mitochondria and receptor for AGEs (RAGE). Treatment of db/db mice with ALA for 12 wk increased the number of mitochondria with well-organized cristae and fewer autophagosomes. Treatment of RIN-m5F cells with CML-BSA increased the level of RAGE protein and autophagosome formation, caused mitochondrial dysfunction, and decreased insulin secretion. CML-BSA also reduced mitochondrial membrane potential and ATP production, increased ROS and lipid peroxide production, and caused mitochondrial DNA deletions. Elevated fission protein dynamin-related protein 1 (Drp1) level and mitochondrial fragmentation demonstrated the unbalance of mitochondrial fusion and fission in CML-BSA-treated cells. Additionally, increased levels of Parkin and PTEN-induced putative kinase 1 protein suggest that fragmented mitochondria were associated with increased mitophagic activity, and ALA attenuated the CML-BSA-induced mitophage formation. Our study demonstrated that CML-BSA induced mitochondrial dysfunction and mitophagy in pancreatic β-cells. The findings from this study suggest that increased concentration of AGEs may damage β-cells and reduce insulin secretion.

  9. Molecular Mechanisms of Insulin Secretion and Insulin Action.

    ERIC Educational Resources Information Center

    Flatt, Peter R.; Bailey, Clifford J.

    1991-01-01

    Information and current ideas on the factors regulating insulin secretion, the mechanisms underlying the secretion and biological actions of insulin, and the main characteristics of diabetes mellitus are presented. (Author)

  10. Molecular Mechanisms of Insulin Secretion and Insulin Action.

    ERIC Educational Resources Information Center

    Flatt, Peter R.; Bailey, Clifford J.

    1991-01-01

    Information and current ideas on the factors regulating insulin secretion, the mechanisms underlying the secretion and biological actions of insulin, and the main characteristics of diabetes mellitus are presented. (Author)

  11. MSC attenuate diabetes-induced functional impairment in adipocytes via secretion of insulin-like growth factor-1.

    PubMed

    Gao, Dongyun; Xie, Jiangfan; Zhang, Junhua; Feng, Changjiang; Yao, Bin; Ma, Kui; Li, Jiwei; Wu, Xu; Huang, Sha; Fu, Xiaobing

    2014-09-12

    The function of subcutaneous adipocytes in promoting wound healing is significantly suppressed in diabetic wounds. Recent studies have demonstrated the ability of mesenchymal stem cell (MSC) to ameliorate impaired diabetic wound healing. We hypothesized that MSC function may involve subcutaneous adipocytes. The abnormal function of subcutaneous adipocytes from STZ induced diabetic mice including glucose uptake and free fatty acid (FFA) secretion level were assessed. Then these cells were co-cultured with MSC via a transwell system to observe the changes of metabolic index and glucose transporter four (GLUT4) as well as phosphoinositide 3-kinase/protein kinase (PI3K/AKT) signaling pathway expression. The results of metabolic index suggest that MSC obviously attenuated the diabetes-induced functional impairment. Both mRNA and protein expression analyses showed that PI3K/AKT insulin signaling pathway and GLUT4 expression were up-regulated. These changes were substantially associated with a increased level of insulin-like growth factor-1 (IGF-1) secretion from MSC. These findings suggest that MSC could attenuate abnormal function of diabetic adipocytes by IGF-1secretion, which was more or less associated with the beneficial effects of MSC on improving diabetic wound healing. Copyright © 2014 Elsevier Inc. All rights reserved.

  12. Efficacy of natural diosgenin on cardiovascular risk, insulin secretion, and beta cells in streptozotocin (STZ)-induced diabetic rats.

    PubMed

    Kalailingam, Pazhanichamy; Kannaian, Bhuvaneswari; Tamilmani, Eevera; Kaliaperumal, Rajendran

    2014-09-15

    Costus igneus, has been prescribed for the treatment of diabetic mellitus in India for several years. The aim of this study is to investigate the effects of plant derived diosgenin on cardiovascular risk, insulin secretion, and pancreatic composition through electron microscopical studies of normal and diabetic rats. Diosgenin at a dose of 5 or 10mg/kg per body weight (bw) was orally administered as a single dose per day to diabetic induced rats for a period of 30 days. The effect of diosgenin on blood glucose, HbA1c, PT, APTT, Oxy-LDL, serum lipid profile, electron microscopical studies of pancreas, antioxidant enzymes (in liver, kidney, pancreas) and hepatoprotective enzymes in plasma and liver were measured in normal and diabetic rats. The results showed that fasting blood glucose, PT, APTT, Oxy-LDL, TC, TG, LDL, ALT, AST, ALP, glucose-6-phosphatase, fructose-1,6-bisphosphatase and LPO levels were significantly (p<0.05) increased, whereas HDL, SOD, CAT, GSH and the glycolytic enzyme glucokinase levels were significantly (p<0.05) decreased in the diabetes induced rats and these levels were significantly (p<0.05) reversed back to normal in diabetes induced rats after 30 days of treatment with diosgenin. Electron microscopical studies of the pancreas revealed that the number of beta cells and insulin granules were increased in streptozotocin (STZ) induced diabetic rats after 30 days of treatment with diosgenin. In conclusion, the data obtained from the present study strongly indicate that diosgenin has potential effects on cardiovascular risk, insulin secretion and beta cell regeneration in STZ induced diabetic rats, these results could be useful for new drug development to fight diabetes and its related cardiovascular diseases.

  13. Consumption of a glucose diet enhances the sensitivity of pancreatic islets from adrenalectomized genetically obese (ob/ob) mice to glucose-induced insulin secretion.

    PubMed

    Mistry, A M; Chen, N G; Lee, Y S; Romsos, D R

    1995-03-01

    Consumption of a glucose diet for 4 d markedly elevates plasma insulin concentrations in adrenalectomized ob/ob mice. The present study examined regulation of insulin secretion from perifused pancreatic islets of female adrenalectomized genetically obese (ob/ob) and lean mice fed a glucose diet for 4 d. These mice were fed a high carbohydrate commercial diet for 21 d, or the high carbohydrate commercial diet for 17 d and a purified high glucose diet for the last 4 d of the 21-d feeding period. Adrenalectomy equalized plasma insulin concentrations, pancreatic islet size, rates of insulin secretion in response to 20 mmol/L glucose and insulin mRNA relative abundance in ob/ob and lean mice fed the commercial diet, but the threshold for glucose-induced insulin secretion determined by a linear glucose gradient remained lower in islets from adrenalectomized ob/ob mice than in those from lean mice (3.8 +/- 0.1 vs. 4.9 +/- 0.2 mmol/L glucose), and addition of acetylcholine to the perifusate lowered the threshold to only 2.0 +/- 0.1 mmol/L glucose in islets from ob/ob mice vs. 3.3 +/- 0.1 mmol/L glucose in lean mice. Switching from the commercial diet to the glucose diet for 4 d increased plasma insulin concentrations -10-fold in islets from adrenalectomized ob/ob mice without affecting islet size, 20 mmol/L glucose-induced insulin secretion or insulin mRNA abundance. Consumption of the glucose diet did, however, markedly lower the threshold for glucose-induced insulin secretion in islets from adrenalectomized ob/ob mice to approximate the abnormally low glucose thresholds in intact ob/ob mice.(ABSTRACT TRUNCATED AT 250 WORDS)

  14. Mechanisms of estradiol-induced insulin secretion by the G protein-coupled estrogen receptor GPR30/GPER in pancreatic beta-cells.

    PubMed

    Sharma, Geetanjali; Prossnitz, Eric R

    2011-08-01

    Sexual dimorphism and supplementation studies suggest an important role for estrogens in the amelioration of glucose intolerance and diabetes. Because little is known regarding the signaling mechanisms involved in estradiol-mediated insulin secretion, we investigated the role of the G protein-coupled receptor 30, now designated G protein-coupled estrogen receptor (GPER), in activating signal transduction cascades in β-cells, leading to secretion of insulin. GPER function in estradiol-induced signaling in the pancreatic β-cell line MIN6 was assessed using small interfering RNA and GPER-selective ligands (G-1 and G15) and in islets isolated from wild-type and GPER knockout mice. GPER is expressed in MIN6 cells, where estradiol and the GPER-selective agonist G-1 mediate calcium mobilization and activation of ERK and phosphatidylinositol 3-kinase. Both estradiol and G-1 induced insulin secretion under low- and high-glucose conditions, which was inhibited by pretreatment with GPER antagonist G15 as well as depletion of GPER by small interfering RNA. Insulin secretion in response to estradiol and G-1 was dependent on epidermal growth factor receptor and ERK activation and further modulated by phosphatidylinositol 3-kinase activity. In islets isolated from wild-type mice, the GPER antagonist G15 inhibited insulin secretion induced by estradiol and G-1, both of which failed to induce insulin secretion in islets obtained from GPER knockout mice. Our results indicate that GPER activation of the epidermal growth factor receptor and ERK in response to estradiol treatment plays a critical role in the secretion of insulin from β-cells. The results of this study suggest that the activation of downstream signaling pathways by the GPER-selective ligand G-1 could represent a novel therapeutic strategy in the treatment of diabetes.

  15. Structure-function studies of PANDER, an islet specific cytokine inducing cell death of insulin-secreting beta cells.

    PubMed

    Yang, Jichun; Gao, Zhiyong; Robert, Claudia E; Burkhardt, Brant R; Gaweska, Helena; Wagner, Amary; Wu, Jianmei; Greene, Scott R; Young, Robert A; Wolf, Bryan A

    2005-08-30

    PANDER (pancreatic derived factor, FAM3B) is a novel cytokine, present in insulin secretory granules, that induces apoptosis of alpha and beta cells of mouse, rat, and human islets in a dose- and time-dependent manner, and may be implicated in diabetes. PANDER has the predicted secondary structure of 4 alpha-helical bundles with an up-up-down-down topology, and two disulfide bonds. Eleven mutated PANDERs were constructed and expressed in beta-TC3 cells to identify the essential region of PANDER involved in beta-cell death. Beta-cell function was assessed by assays of cell viability and insulin secretion. Based on quantitative real-time RT-PCR all mutant PANDERs had similar mRNA expression levels in beta-TC3 cells. Immunoblotting showed that ten of eleven mutant PANDER proteins were synthesized and detected in beta-TC3 cells. A mutant PANDER with no signal peptide, however, was not expressed. Truncation of helix D alone caused a 40-50% decrease in PANDER's activity, while truncation of both helices C and D resulted in a 75% loss of activity. In contrast, truncation of the N-terminus of PANDER (helix A, the loop between helices A and B, and the first two cysteines) had no effect on PANDER-induced beta-cell death. The third and fourth cysteines of PANDER, C91 and C229, were shown to form one disulfide bond and be functionally important. Finally, the region between Cys91 and Phe152 constitutes the active part of PANDER, based on the demonstration that mutants with truncation of helix B or C caused decreased beta-cell death and did not inhibit insulin secretion, as compared to wild-type PANDER. Hence, helices B and C and the second disulfide bond of PANDER are essential for PANDER-induced beta-cell death.

  16. Defects in beta cell Ca²+ signalling, glucose metabolism and insulin secretion in a murine model of K(ATP) channel-induced neonatal diabetes mellitus.

    PubMed

    Benninger, R K P; Remedi, M S; Head, W S; Ustione, A; Piston, D W; Nichols, C G

    2011-05-01

    Mutations that render ATP-sensitive potassium (K(ATP)) channels insensitive to ATP inhibition cause neonatal diabetes mellitus. In mice, these mutations cause insulin secretion to be lost initially and, as the disease progresses, beta cell mass and insulin content also disappear. We investigated whether defects in calcium signalling alone are sufficient to explain short-term and long-term islet dysfunction. We examined the metabolic, electrical and insulin secretion response in islets from mice that become diabetic after induction of ATP-insensitive Kir6.2 expression. To separate direct effects of K(ATP) overactivity on beta cell function from indirect effects of prolonged hyperglycaemia, normal glycaemia was maintained by protective exogenous islet transplantation. In endogenous islets from protected animals, glucose-dependent elevations of intracellular free-calcium activity ([Ca(2+)](i)) were severely blunted. Insulin content of these islets was normal, and sulfonylureas and KCl stimulated increased [Ca(2+)](i). In the absence of transplant protection, [Ca(2+)](i) responses were similar, but glucose metabolism and redox state were dramatically altered; sulfonylurea- and KCl-stimulated insulin secretion was also lost, because of systemic effects induced by long-term hyperglycaemia and/or hypoinsulinaemia. In both cases, [Ca(2+)](i) dynamics were synchronous across the islet. After reduction of gap-junction coupling, glucose-dependent [Ca(2+)](i) and insulin secretion was partially restored, indicating that excitability of weakly expressing cells is suppressed by cells expressing mutants, via gap-junctions. The primary defect in K(ATP)-induced neonatal diabetes mellitus is failure of glucose metabolism to elevate [Ca(2+)](i), which suppresses insulin secretion and mildly alters islet glucose metabolism. Loss of insulin content and mitochondrial dysfunction are secondary to the long-term hyperglycaemia and/or hypoinsulinaemia that result from the absence of glucose

  17. Hypothalamic astroglial connexins are required for brain glucose sensing-induced insulin secretion.

    PubMed

    Allard, Camille; Carneiro, Lionel; Grall, Sylvie; Cline, Brandon H; Fioramonti, Xavier; Chrétien, Chloé; Baba-Aissa, Fawzia; Giaume, Christian; Pénicaud, Luc; Leloup, Corinne

    2014-02-01

    Hypothalamic glucose detection participates in maintaining glycemic balance, food intake, and thermogenesis. Although hypothalamic neurons are the executive cells involved in these responses, there is increasing evidence that astrocytes participate in glucose sensing (GS); however, it is unknown whether astroglial networking is required for glucose sensitivity. Astroglial connexins 30 and 43 (Cx30 and Cx43) form hexameric channels, which are apposed in gap junctions, allowing for the intercellular transfer of small molecules such as glucose throughout the astroglial networks. Here, we hypothesized that hypothalamic glucose sensitivity requires these connexins. First, we showed that both Cxs are enriched in the rat hypothalamus, with highly concentrated Cx43 expression around blood vessels of the mediobasal hypothalamus (MBH). Both fasting and high glycemic levels rapidly altered the protein levels of MBH astroglial connexins, suggesting cross talk within the MBH between glycemic status and the connexins' ability to dispatch glucose. Finally, the inhibition of MBH Cx43 (by transient RNA interference) attenuated hypothalamic glucose sensitivity in rats, which was demonstrated by a pronounced decreased insulin secretion in response to a brain glucose challenge. These results illustrate that astroglial connexins contribute to hypothalamic GS.

  18. Model-Based Quantification of Glucagon-Like Peptide-1–Induced Potentiation of Insulin Secretion in Response to a Mixed Meal Challenge

    PubMed Central

    Dalla Man, Chiara; Micheletto, Francesco; Sathananthan, Matheni; Vella, Adrian

    2016-01-01

    Abstract Background: Glucagon-like peptide-1 (GLP-1) is a powerful insulin secretagogue that is secreted in response to meal ingestion. The ability to quantify the effect of GLP-1 on insulin secretion could provide insights into the pathogenesis and treatment of diabetes. We used a modification of a model of GLP-1 action on insulin secretion using data from a hyperglycemic clamp with concomitant GLP-1 infusion. We tested this model using data from a mixed meal test (MMT), thereby measuring GLP-1-induced potentiation of insulin secretion in response to a meal. Materials and Methods: The GLP-1 model is based on the oral C-peptide minimal model and assumes that over-basal insulin secretion depends linearly on GLP-1 concentration through the parameter Π, representing the β-cell sensitivity to GLP-1. The model was tested on 62 subjects across the spectrum of glucose tolerance (age, 53 ± 1 years; body mass index, 29.7 ± 0.6 kg/m2) studied with an MMT and provided a precise estimate of both β-cell responsivity and Π indices. By combining Π with a measure of L-cell responsivity to glucose, one obtains a potentiation index (PI) (i.e., a measure of the L-cell's function in relation to prevailing β-cell sensitivity to GLP-1). Results: Model-based measurement of GLP-1-induced insulin secretion demonstrates that the PI is significantly reduced in people with impaired glucose tolerance, compared with those with normal glucose tolerance. Conclusions: We describe a model that can quantitate the GLP-1-based contribution to insulin secretion in response to meal ingestion. This methodology will allow a better understanding of β-cell function at various stages of glucose tolerance. PMID:26756104

  19. Regulation of glucose- and mitochondrial fuel-induced insulin secretion by a cytosolic protein histidine phosphatase in pancreatic beta-cells.

    PubMed

    Kamath, Vasudeva; Kyathanahalli, Chandrashekara N; Jayaram, Bhavaani; Syed, Ismail; Olson, Lawrence Karl; Ludwig, Katrin; Klumpp, Susanne; Krieglstein, Josef; Kowluru, Anjaneyulu

    2010-08-01

    We report localization of a cytosolic protein histidine phosphatase (PHP; approximately 16 kDa) in INS 832/13 cells, normal rat islets, and human islets. siRNA-mediated knockdown of PHP markedly reduced glucose- or mitochondrial fuel-induced but not KCl-induced insulin secretion. siRNA-mediated knockdown of PHP also attenuated mastoparan-induced insulin secretion, suggesting its participation in G protein-sensitive signaling steps, leading to insulin secretion. Functional assays revealed that the beta-cell PHP catalyzes the dephosphorylation of ATP-citrate lyase (ACL). Silencing of PHP expression markedly reduced ACL activity, suggesting functional regulation of ACL by PHP in beta-cells. Coimmunoprecipitation studies revealed modest effects of glucose on the interaction between PHP and ACL. Confocal microscopic evidence indicated that glucose promotes association between ACL and nm23-H1, a known kinase histidine kinase, but not between PHP and ACL. Furthermore, metabolic viability of INS 832/13 cells was resistant to siRNA-PHP, suggesting no regulatory roles of PHP in cell viability. Finally, long-term exposure (24 h) of INS 832/13 cells or rat islets to high glucose (30 mM) increased the expression of PHP. Such increases in PHP expression were also seen in islets derived from the Zucker diabetic fatty rat compared with islets from the lean control animals. Together, these data implicate regulatory roles for PHP in a G protein-sensitive step involved in nutrient-induced insulin secretion. In light of the current debate on putative regulatory roles of ACL in insulin secretion, additional studies are needed to precisely identify the phosphoprotein substrate(s) for PHP in the cascade of events leading to nutrient-induced insulin secretion.

  20. Regulation of glucose- and mitochondrial fuel-induced insulin secretion by a cytosolic protein histidine phosphatase in pancreatic β-cells

    PubMed Central

    Kamath, Vasudeva; Kyathanahalli, Chandrashekara N.; Jayaram, Bhavaani; Syed, Ismail; Olson, Lawrence Karl; Ludwig, Katrin; Klumpp, Susanne; Krieglstein, Josef

    2010-01-01

    We report localization of a cytosolic protein histidine phosphatase (PHP; ∼16 kDa) in INS 832/13 cells, normal rat islets, and human islets. siRNA-mediated knockdown of PHP markedly reduced glucose- or mitochondrial fuel-induced but not KCl-induced insulin secretion. siRNA-mediated knockdown of PHP also attenuated mastoparan-induced insulin secretion, suggesting its participation in G protein-sensitive signaling steps, leading to insulin secretion. Functional assays revealed that the β-cell PHP catalyzes the dephosphorylation of ATP-citrate lyase (ACL). Silencing of PHP expression markedly reduced ACL activity, suggesting functional regulation of ACL by PHP in β-cells. Coimmunoprecipitation studies revealed modest effects of glucose on the interaction between PHP and ACL. Confocal microscopic evidence indicated that glucose promotes association between ACL and nm23-H1, a known kinase histidine kinase, but not between PHP and ACL. Furthermore, metabolic viability of INS 832/13 cells was resistant to siRNA-PHP, suggesting no regulatory roles of PHP in cell viability. Finally, long-term exposure (24 h) of INS 832/13 cells or rat islets to high glucose (30 mM) increased the expression of PHP. Such increases in PHP expression were also seen in islets derived from the Zucker diabetic fatty rat compared with islets from the lean control animals. Together, these data implicate regulatory roles for PHP in a G protein-sensitive step involved in nutrient-induced insulin secretion. In light of the current debate on putative regulatory roles of ACL in insulin secretion, additional studies are needed to precisely identify the phosphoprotein substrate(s) for PHP in the cascade of events leading to nutrient-induced insulin secretion. PMID:20501872

  1. Insulin-induced hypoglycemia stimulates corticotropin-releasing factor and arginine vasopressin secretion into hypophysial portal blood of conscious, unrestrained rams.

    PubMed Central

    Caraty, A; Grino, M; Locatelli, A; Guillaume, V; Boudouresque, F; Conte-Devolx, B; Oliver, C

    1990-01-01

    Insulin-induced hypoglycemia (IIH) is a strong stimulator of pituitary ACTH secretion. The mechanisms by which IIH activates the corticotrophs are still controversial. Indeed, in rats the variations of corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) secretion in hypophysial portal blood (HPB) during IIH have been diversely appreciated. This may be due to the stressful conditions required for portal blood collection in rats. We studied the effects of IIH on the secretion of CRF and AVP in HPB and on the release of ACTH and cortisol in peripheral plasma in conscious, unrestrained, castrated rams. After the injection of a low (0.2 IU/kg) or high dose (2 IU/kg) of insulin, ACTH and cortisol levels in peripheral plasma increased in a dose-related manner. After injection of the low dose of insulin, CRF and AVP secretion in HPB were equally stimulated. After injection of the high dose of insulin, CRF secretion was further stimulated, while AVP release was dramatically increased. These results suggest that when the hypoglycemia is moderate, CRF is the main factor triggering ACTH release, and that the increased AVP secretion potentiates the stimulatory effect of CRF. When hypoglycemia is deeper, AVP secretion becomes predominant and may by itself stimulate ACTH release. Images PMID:2161426

  2. Pancreatic-derived factor (FAM3B), a novel islet cytokine, induces apoptosis of insulin-secreting beta-cells.

    PubMed

    Cao, Xiaopei; Gao, Zhiyong; Robert, Claudia E; Greene, Scott; Xu, Gang; Xu, Weizhen; Bell, Ewan; Campbell, Don; Zhu, Yuan; Young, Robert; Trucco, Matteo; Markmann, James F; Naji, Ali; Wolf, Bryan A

    2003-09-01

    PANDER (PANcreatic DERived factor, FAM3B), a newly discovered secreted cytokine, is specifically expressed at high levels in the islets of Langerhans of the endocrine pancreas. To evaluate the role of PANDER in beta-cell function, we investigated the effects of PANDER on rat, mouse, and human pancreatic islets; the beta-TC3 cell line; and the alpha-TC cell line. PANDER protein was present in alpha- and beta-cells of pancreatic islets, insulin-secreting beta-TC3 cells, and glucagon-secreting alpha-TC cells. PANDER induced islet cell death in rat and human islets. Culture of beta-TC3 cells with recombinant PANDER had a dose-dependent inhibitory effect on cell viability. This effect was also time-dependent. PANDER caused apoptosis of beta-cells as assessed by electron microscopy, annexin V fluorescent staining, and flow-cytometric terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. PANDER did not affect cytosolic Ca(2+) levels or nitric oxide levels. However, PANDER activated caspase-3. Hence, PANDER may have a role in the process of pancreatic beta-cell apoptosis.

  3. Triphenyltin impairs insulin secretion by decreasing glucose-induced NADP(H) and ATP production in hamster pancreatic β-cells.

    PubMed

    Miura, Yoshikazu; Hori, Yuichi; Kimura, Shinzo; Hachiya, Hiroyuki; Sakurai, Yuichirou; Inoue, Kenichi; Sawada, Tokihiko; Kubota, Keiichi

    2012-09-28

    Oral administration of triphenyltin chloride (TPT) (6 mg/100g body weight) inhibits insulin secretion by decreasing glucose-induced cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) in pancreatic β-cells of the hamster. To test the possibility that the abnormal level of the [Ca(2+)](i) induced by TPT administration could be due to a defect in the metabolic signal of glucose in the β-cells, we tested the effects of TPT administration on the glucose-induced NAD(P)H and ATP production, and on the changes of membrane potential and [Ca(2+)](i) by glucose and high K(+) in the β-cells. The [Ca(2+)](i) was measured in islet cells loaded with fura-2. TPT administration significantly reduced the NAD(P)H and ATP production, the depolarization of plasma membrane, and insulin secretion by 15 mM glucose in islet cells. TPT administration also reduced the insulin secretion by 10mM dihydroxyacetone and glyceraldehyde. However, TPT administration did not affect the increase of [Ca(2+)](i) and the insulin secretion by 30 mMK(+) or 100 μM tolbutamide, and the membrane potential by 30 mMK(+), and the insulin secretion by 10mM α-ketoisocaproic acid and 0.5mM formycin A, an analog of ATP in the presence of 15 mM glucose. These results suggested that the pathogenesis of TPT-induced hyperglycemia in hamster involves the reduction of [Ca(2+)](i) and insulin secretion in response to K(ATP) channel-dependent depolarization, which is related to the decrease of NAD(P)H and ATP production in pancreatic islet cells after glucose metabolism.

  4. Intracellular alkalinization by phosphate uptake via type III sodium-phosphate cotransporter participates in high-phosphate-induced mitochondrial oxidative stress and defective insulin secretion.

    PubMed

    Nguyen, Tuyet Thi; Quan, Xianglan; Xu, Shanhua; Das, Ranjan; Cha, Seung-Kuy; Kong, In Deok; Shong, Minho; Wollheim, Claes B; Park, Kyu-Sang

    2016-12-01

    Elevated plasma levels of inorganic phosphate (Pi) are harmful, causing, among other complications, vascular calcification and defective insulin secretion. The underlying molecular mechanisms of these complications remain poorly understood. We demonstrated the role of Pi transport across the plasmalemma on Pi toxicity in INS-1E rat clonal β cells and rat pancreatic islet cells. Type III sodium-phosphate cotransporters (NaPis) are the predominant Pi transporters expressed in insulin-secreting cells. Transcript and protein levels of sodium-dependent phosphate transporter 1 and 2 (PiT-1 and -2), isotypes of type III NaPi, were up-regulated by high-Pi incubation. In patch-clamp experiments, extracellular Pi elicited a Na(+)-dependent, inwardly rectifying current, which was markedly reduced under acidic extracellular conditions. Cellular uptake of Pi elicited cytosolic alkalinization; intriguingly, this pH change facilitated Pi transport into the mitochondrial matrix. Increased mitochondrial Pi uptake accelerated superoxide generation, mitochondrial permeability transition (mPT), and endoplasmic reticulum stress-mediated translational attenuation, leading to reduced insulin content and impaired glucose-stimulated insulin secretion. Silencing of PiT-1/2 prevented Pi-induced superoxide generation and mPT, and restored insulin secretion. We propose that Pi transport across the plasma membrane and consequent cytosolic alkalinization could be a therapeutic target for protection from Pi toxicity in insulin-secreting cells, as well as in other cell types.-Nguyen, T. T., Quan, X., Xu, S., Das, R., Cha, S.-K., Kong, I. D., Shong, M., Wollheim, C. B., Park, K.-S. Intracellular alkalinization by phosphate uptake via type III sodium-phosphate cotransporter participates in high-phosphate-induced mitochondrial oxidative stress and defective insulin secretion. © FASEB.

  5. Dietary soy isoflavones increase insulin secretion and prevent the development of diabetic cataracts in streptozotocin-induced diabetic rats.

    PubMed

    Lu, Mei-Ping; Wang, Rui; Song, Xiuyuan; Chibbar, Rajni; Wang, Xiaoxia; Wu, Lingyun; Meng, Qing H

    2008-07-01

    Soy isoflavone-containing diets have been reported to be beneficial in diabetes. This present study investigated the hypoglycemic effects of isoflavones in streptozotocin (STZ)-induced diabetes. Diabetes was induced in male Sprague-Dawley rats by intraperitoneal injection of 100 mg/kg STZ. Diabetic rats were then randomly divided into 3 groups and received a special diet supplemented with casein (control), low-isoflavone soy (LIS) protein, and high-isoflavone soy protein (HIS) for 8 weeks. Compared with the control or LIS groups, those rats on the HIS diet had significantly increased body weight and serum insulin levels and reduced serum glucose and methylglyoxal levels. Serum glutathione levels were also increased in rats given the HIS diet compared with those in the control or LIS (P < .01). Serum high-density lipoprotein cholesterol level was significantly higher in HIS-fed rats than that of the control or LIS rats (P < .05). More importantly, the death rate and incidence of cataracts in the diabetic rats were markedly decreased in the HIS group. In conclusion, ingestion of high-isoflavone soy protein not only lowers glucose levels but also reduces the incidence of cataracts in diabetic rats. The beneficial effects of soy isoflavones are attributed to increased insulin secretion, a better glycemic control, and antioxidant protection.

  6. Quercetin induces insulin secretion by direct activation of L-type calcium channels in pancreatic beta cells

    PubMed Central

    Bardy, G; Virsolvy, A; Quignard, J F; Ravier, M A; Bertrand, G; Dalle, S; Cros, G; Magous, R; Richard, S; Oiry, C

    2013-01-01

    Background and Purpose Quercetin is a natural polyphenolic flavonoid that displays anti-diabetic properties in vivo. Its mechanism of action on insulin-secreting beta cells is poorly documented. In this work, we have analysed the effects of quercetin both on insulin secretion and on the intracellular calcium concentration ([Ca2+]i) in beta cells, in the absence of any co-stimulating factor. Experimental Approach Experiments were performed on both INS-1 cell line and rat isolated pancreatic islets. Insulin release was quantified by the homogeneous time-resolved fluorescence method. Variations in [Ca2+]i were measured using the ratiometric fluorescent Ca2+ indicator Fura-2. Ca2+ channel currents were recorded with the whole-cell patch-clamp technique. Key Results Quercetin concentration-dependently increased insulin secretion and elevated [Ca2+]i. These effects were not modified by the SERCA inhibitor thapsigargin (1 μmol·L−1), but were nearly abolished by the L-type Ca2+ channel antagonist nifedipine (1 μmol·L−1). Similar to the L-type Ca2+ channel agonist Bay K 8644, quercetin enhanced the L-type Ca2+ current by shifting its voltage-dependent activation towards negative potentials, leading to the increase in [Ca2+]i and insulin secretion. The effects of quercetin were not inhibited in the presence of a maximally active concentration of Bay K 8644 (1 μmol·L−1), with the two drugs having cumulative effects on [Ca2+]i. Conclusions and Implications Taken together, our results show that quercetin stimulates insulin secretion by increasing Ca2+ influx through an interaction with L-type Ca2+ channels at a site different from that of Bay K 8644. These data contribute to a better understanding of quercetin's mechanism of action on insulin secretion. PMID:23530660

  7. Neuropeptide Y and somatostatin inhibit insulin secretion through different mechanisms

    PubMed Central

    Schwetz, Tara A.; Ustione, Alessandro

    2013-01-01

    Pancreatic β-cells regulate glucose homeostasis by secreting insulin in response to glucose elevation and G protein-coupled receptor (GPCR) activation. Neuropeptide Y (NPY) and somatostatin (SST) attenuate insulin secretion through Gi activation of Y1 and SSTR1&5 receptors, respectively. The downstream pathways altered by NPY and SST are poorly understood. Thus, we investigated these underlying mechanisms. NPY and SST increase cellular redox potential, suggesting that their inhibitory effect may not be mediated through metabolic inhibition. NPY does not affect intracellular calcium ([Ca2+]i) activity upon glucose stimulation, whereas SST alters this response. Gβγ-subunit inhibition by gallein attenuates insulin secretion but does not alter metabolism or [Ca2+]i. mSIRK-induced Gβγ activation does not modulate glucose metabolism but increases [Ca2+]i activity and potentiates insulin release. Cotreatment with gallein and NPY or SST reduces insulin secretion to levels similar to that of gallein alone. mSIRK and NPY cotreatment potentiates insulin secretion similarly to mSIRK alone, whereas mSIRK and SST treatment decreases insulin release. The data support a model where SST attenuates secretion through Gβγ inhibition of Ca2+ activity, while NPY activates a Ca2+-independent pathway mediated by Gα. GPCR ligands signal through multiple pathways to inhibit insulin secretion, and determining these mechanisms could lead to novel diabetic therapies. PMID:23211512

  8. Neuropeptide Y and somatostatin inhibit insulin secretion through different mechanisms.

    PubMed

    Schwetz, Tara A; Ustione, Alessandro; Piston, David W

    2013-01-15

    Pancreatic β-cells regulate glucose homeostasis by secreting insulin in response to glucose elevation and G protein-coupled receptor (GPCR) activation. Neuropeptide Y (NPY) and somatostatin (SST) attenuate insulin secretion through G(i) activation of Y(1) and SSTR(1&5) receptors, respectively. The downstream pathways altered by NPY and SST are poorly understood. Thus, we investigated these underlying mechanisms. NPY and SST increase cellular redox potential, suggesting that their inhibitory effect may not be mediated through metabolic inhibition. NPY does not affect intracellular calcium ([Ca(2+)](i)) activity upon glucose stimulation, whereas SST alters this response. G(βγ)-subunit inhibition by gallein attenuates insulin secretion but does not alter metabolism or [Ca(2+)](i). mSIRK-induced G(βγ) activation does not modulate glucose metabolism but increases [Ca(2+)](i) activity and potentiates insulin release. Cotreatment with gallein and NPY or SST reduces insulin secretion to levels similar to that of gallein alone. mSIRK and NPY cotreatment potentiates insulin secretion similarly to mSIRK alone, whereas mSIRK and SST treatment decreases insulin release. The data support a model where SST attenuates secretion through G(βγ) inhibition of Ca(2+) activity, while NPY activates a Ca(2+)-independent pathway mediated by G(α). GPCR ligands signal through multiple pathways to inhibit insulin secretion, and determining these mechanisms could lead to novel diabetic therapies.

  9. Insulin secretion in children with growth retardation.

    PubMed

    Boscherini, B; Finocchi, G; Lostia, O; Mancuso, G; Montani, P; Pasquino, A M; Rezza, E; Rocchio, J; Taggi, F; Zorretta, D

    1977-12-30

    The effect of tolbutamide administration on insulin secretion was studied in 69 children with growth retardation. Diminished insulin secretion was found in all the patients, compared to the control group. This insulin deficit was most evident in patients with isolated, total GH deficiency and least evident in children with idiopathic short stature. Intermediate values were found in dwarfism due to isolated, partial GH deficiency. These results favour the hypothesis that hypoinsulinism contributes to the somatotropin deficiency in causing growth retardation.

  10. Monomethylated-adenines potentiate glucose-induced insulin production and secretion via inhibition of phosphodiesterase activity in rat pancreatic islets.

    PubMed

    Boland, Brandon B; Alarcón, Cristina; Ali, Almas; Rhodes, Christopher J

    2015-01-01

    Monomethyladenines have effects on DNA repair, G-protein-coupled receptor antagonism and autophagy. In islet ß-cells, 3-methyladenine (3-MA) has been implicated in DNA-repair and autophagy, but its mechanism of action is unclear. Here, the effect of monomethylated adenines was examined in rat islets. 3-MA, N6-methyladenine (N6-MA) and 9-methyladenine (9-MA), but not 1- or 7-monomethylated adenines, specifically potentiated glucose-induced insulin secretion (3-4 fold; p ≤ 0.05) and proinsulin biosynthesis (∼2-fold; p ≤ 0.05). Using 3-MA as a 'model' monomethyladenine, it was found that 3-MA augmented [cAMP]i accumulation (2-3 fold; p ≤ 0.05) in islets within 5 minutes. The 3-, N6- and 9-MA also enhanced glucose-induced phosphorylation of the cAMP/protein kinase-A (PKA) substrate cAMP-response element binding protein (CREB). Treatment of islets with pertussis or cholera toxin indicated 3-MA mediated elevation of [cAMP]i was not mediated via G-protein-coupled receptors. Also, 3-MA did not compete with 9-cyclopentyladenine (9-CPA) for adenylate cyclase inhibition, but did for the pan-inhibitor of phosphodiesterase (PDE), 3-isobutyl-1-methylxanthine (IBMX). Competitive inhibition experiments with PDE-isoform specific inhibitors suggested 3-MA to have a preference for PDE4 in islet ß-cells, but this was likely reflective of PDE4 being the most abundant PDE isoform in ß-cells. In vitro enzyme assays indicated that 3-, N6- and 9-MA were capable of inhibiting most PDE isoforms found in ß-cells. Thus, in addition to known inhibition of phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3'K)/m Target of Rapamycin (mTOR) signaling, 3-MA also acts as a pan-phosphodiesterase inhibitor in pancreatic ß-cells to elevate [cAMP]i and then potentiate glucose-induced insulin secretion and production in parallel.

  11. RANTES (CCL5) reduces glucose-dependent secretion of glucagon-like peptides 1 and 2 and impairs glucose-induced insulin secretion in mice.

    PubMed

    Pais, Ramona; Zietek, Tamara; Hauner, Hans; Daniel, Hannelore; Skurk, Thomas

    2014-08-01

    Type 2 diabetes is associated with elevated circulating levels of the chemokine RANTES and with decreased plasma levels of the incretin hormone glucagon-like peptide 1 (GLP-1). GLP-1 is a peptide secreted from intestinal L-cells upon nutrient ingestion. It enhances insulin secretion from pancreatic β-cells and protects from β-cell loss but also promotes satiety and weight loss. In search of chemokines that may reduce GLP-1 secretion we identified RANTES and show that it reduces glucose-stimulated GLP-1 secretion in the human enteroendocrine cell line NCI-H716, blocked by the antagonist Met-RANTES, and in vivo in mice. RANTES exposure to mouse intestinal tissues lowers transport function of the intestinal glucose transporter SGLT1, and administration in mice reduces plasma GLP-1 and GLP-2 levels after an oral glucose load and thereby impairs insulin secretion. These data show that RANTES is involved in altered secretion of glucagon-like peptide hormones most probably acting through SGLT1, and our study identifies the RANTES-receptor CCR1 as a potential target in diabetes therapy.

  12. Suppression of Insulin Production and Secretion by a Decretin Hormone

    PubMed Central

    Alfa, Ronald W.; Park, Sangbin; Skelly, Kathleen-Rose; Poffenberger, Gregory; Jain, Nimit; Gu, Xueying; Kockel, Lutz; Wang, Jing; Liu, Yinghua; Powers, Alvin C.; Kim, Seung K.

    2015-01-01

    SUMMARY Decretins, hormones induced by fasting that suppress insulin production and secretion, have been postulated from classical human metabolic studies. From genetic screens, we identified Drosophila Limostatin (Lst), a peptide hormone that suppresses insulin secretion. Lst is induced by nutrient restriction in gut-associated endocrine cells. limostatin deficiency led to hyperinsulinemia, hypoglycemia and excess adiposity. A conserved 15-residue polypeptide encoded by limostatin suppressed secretion by insulin-producing cells. Targeted knockdown of CG9918, a Drosophila orthologue of Neuromedin U receptors (NMUR), in insulin-producing cells phenocopied limostatin deficiency, and attenuated insulin suppression by purified Lst, suggesting CG9918 encodes an Lst receptor. NMUR1 is expressed in islet β-cells, and purified NMU suppresses insulin secretion from human islets. A human mutant NMU variant that co-segregates with familial early-onset obesity and hyperinsulinemia fails to suppress insulin secretion. We propose Lst as an index member of an ancient hormone class called decretins, which suppress insulin output. PMID:25651184

  13. Effects of aldosterone on insulin sensitivity and secretion.

    PubMed

    Luther, James M

    2014-12-01

    Dr. Conn originally reported an increased risk of diabetes in patients with hyperaldosteronism in the 1950s, although the mechanism remains unclear. Aldosterone-induced hypokalemia was initially described to impair glucose tolerance by impairing insulin secretion. Correction of hypokalemia by potassium supplementation only partially restored insulin secretion and glucose tolerance, however. Aldosterone also impairs glucose-stimulated insulin secretion in isolated pancreatic islets via reactive oxygen species in a mineralocorticoid receptor-independent manner. Aldosterone-induced mineralocorticoid receptor activation also impairs insulin sensitivity in adipocytes and skeletal muscle. Aldosterone may produce insulin resistance secondarily by altering potassium, increasing inflammatory cytokines, and reducing beneficial adipokines such as adiponectin. Renin-angiotensin system antagonists reduce circulating aldosterone concentrations and also the risk of type 2 diabetes in clinical trials. These data suggest that primary and secondary hyperaldosteronism may contribute to worsening glucose tolerance by impairing insulin sensitivity or insulin secretion in humans. Future studies should define the effects of MR antagonists and aldosterone on insulin secretion and sensitivity in humans.

  14. Suppression of insulin production and secretion by a decretin hormone.

    PubMed

    Alfa, Ronald W; Park, Sangbin; Skelly, Kathleen-Rose; Poffenberger, Gregory; Jain, Nimit; Gu, Xueying; Kockel, Lutz; Wang, Jing; Liu, Yinghua; Powers, Alvin C; Kim, Seung K

    2015-02-03

    Decretins, hormones induced by fasting that suppress insulin production and secretion, have been postulated from classical human metabolic studies. From genetic screens, we identified Drosophila Limostatin (Lst), a peptide hormone that suppresses insulin secretion. Lst is induced by nutrient restriction in gut-associated endocrine cells. limostatin deficiency led to hyperinsulinemia, hypoglycemia, and excess adiposity. A conserved 15-residue polypeptide encoded by limostatin suppressed secretion by insulin-producing cells. Targeted knockdown of CG9918, a Drosophila ortholog of Neuromedin U receptors (NMURs), in insulin-producing cells phenocopied limostatin deficiency and attenuated insulin suppression by purified Lst, suggesting CG9918 encodes an Lst receptor. NMUR1 is expressed in islet β cells, and purified NMU suppresses insulin secretion from human islets. A human mutant NMU variant that co-segregates with familial early-onset obesity and hyperinsulinemia fails to suppress insulin secretion. We propose Lst as an index member of an ancient hormone class called decretins, which suppress insulin output.

  15. Beta-endorphin-induced inhibition and stimulation of insulin secretion in normal humans is glucose dependent.

    PubMed

    Giugliano, D; Cozzolino, D; Salvatore, T; Torella, R; D'Onofrio, F

    1988-09-01

    This study evaluated the effect of human beta-endorphin on pancreatic hormone levels and their responses to nutrient challenges in normal subjects. Infusion of 0.5 mg/h beta-endorphin caused a significant rise in plasma glucose concentrations preceded by a significant increase in peripheral glucagon levels. No changes occurred in the plasma concentrations of insulin and C-peptide. Acute insulin and C-peptide responses to intravenous pulses of different glucose amounts (0.33 g/kg and 5 g) and arginine (3 g) were significantly reduced by beta-endorphin infusion (P less than .01). This effect was associated with a significant reduction of the glucose disappearance rates, suggesting that the inhibition of insulin was of biological relevance. beta-Endorphin also inhibited glucose suppression of glucagon levels and augmented the glucagon response to arginine. To verify whether the modification of prestimulus glucose level could be important in these hormonal responses to beta-endorphin, basal plasma glucose concentrations were raised by a primed (0.5 g/kg) continuous (20 mg kg-1.min-1) glucose infusion. After stabilization of plasma glucose levels (350 +/- 34 mg/dl, t = 120 min), beta-endorphin infusion caused an immediate and marked increase in plasma insulin level (peak response 61 +/- 9 microU/ml, P less than .01), which remained elevated even after the discontinuation of opioid infusion. Moreover, the acute insulin response to a glucose pulse (0.33 g/kg i.v.) given during beta-endorphin infusion during hyperglycemia was significantly higher than the response obtained during euglycemia (171 +/- 32 vs. 41 +/- 7 microU/ml, P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

  16. Mechanism by which cyproheptadine inhibits insulin secretion.

    PubMed Central

    Donatsch, P.; Lowe, D. A.; Richardson, B. P.; Taylor, P.

    1980-01-01

    1 Isolated islets of Langerhans from the rat have been used in studies designed to elucidate the mechanism by which cyproheptadine inhibits insulin secretion. 2 D-Glucose and tolbutamide, both of which require extracellular Ca2+ to produce insulin release, failed to evoke a secretory response from islets pretreated with cyproheptadine. Conversely veratridine, the calcium ionophore A23187 and theophylline, all of which are capable of mobilizing sufficient intracellular Ca2+ to evoke insulin secretion in the absence of extracellular Ca2+, produced similar responses from cyproheptadine pretreated and control islets. 3 Cyproheptadine completely inhibited Ca2+ uptake induced by D-glucose and high Ko+, two agents which depolarize the islet beta-cell membrane, whilst Ca2+ uptake elicited by removal of extracellular Na+ (i.e. Na+-Ca2+ counter transport) was only slightly reduced. 4 A significant increase in Na+ uptake produced by veratridine was sensitive to tetrodoxin but only partially reduced by cyproheptadine. 5 These results suggest that cyproheptadine inhibits depolarization-dependent calcium entry into pancreatic beta-cells. PMID:7002245

  17. Insulin and Glucagon Secretion In Vitro

    NASA Technical Reports Server (NTRS)

    Rajan, Arun S.

    1998-01-01

    Long-duration space flight is associated with many physiological abnormalities in astronauts. In particular, altered regulation of the hormones insulin and glucagon may contribute to metabolic disturbances such as increased blood sugar levels, which if persistently elevated result in toxic effects. These changes are also observed in the highly prevalent disease diabetes, which affects 16 million Americans and consumes over $100 billion in annual healthcare costs. By mimicking the microgravity environment of space in the research laboratory using a NASA-developed bioreactor, one can study the physiology of insulin and glucagon secretion and determine if there are alterations in these cellular processes. The original specific objectives of the project included: (1) growing ('cell culture') of pancreatic islet beta and alpha cells that secrete insulin and glucagon respectively, in the NASA bioreactor; (2) examination of the effects of microgravity on insulin and glucagon secretion; and (3) study of molecular mechanisms of insulin and glucagon secretion if altered by microgravity.

  18. Cholesterol reduction ameliorates glucose-induced calcium handling and insulin secretion in islets from low-density lipoprotein receptor knockout mice.

    PubMed

    Souza, J C; Vanzela, E C; Ribeiro, R A; Rezende, L F; de Oliveira, C A; Carneiro, E M; Oliveira, H C F; Boschero, A C

    2013-04-01

    Changes in cellular cholesterol level may contribute to beta cell dysfunction. Islets from low density lipoprotein receptor knockout (LDLR(-/-)) mice have higher cholesterol content and secrete less insulin than wild-type (WT) mice. Here, we investigated the association between cholesterol content, insulin secretion and Ca(2+) handling in these islets. Isolated islets from both LDLR(-/-) and WT mice were used for measurements of insulin secretion (radioimmunoassay), cholesterol content (fluorimetric assay), cytosolic Ca(2+) level (fura-2AM) and SNARE protein expression (VAMP-2, SNAP-25 and syntaxin-1A). Cholesterol was depleted by incubating the islets with increasing concentrations (0-10mmol/l) of methyl-beta-cyclodextrin (MβCD). The first and second phases of glucose-stimulated insulin secretion (GSIS) were lower in LDLR(-/-) than in WT islets, paralleled by an impairment of Ca(2+) handling in the former. SNAP-25 and VAMP-2, but not syntaxin-1A, were reduced in LDLR(-/-) compared with WT islets. Removal of excess cholesterol from LDLR(-/-) islets normalized glucose- and tolbutamide-induced insulin release. Glucose-stimulated Ca(2+) handling was also normalized in cholesterol-depleted LDLR(-/-) islets. Cholesterol removal from WT islets by 0.1 and 1.0mmol/l MβCD impaired both GSIS and Ca(2+) handling. In addition, at 10mmol/l MβCD WT islet showed a loss of membrane integrity and higher DNA fragmentation. Abnormally high (LDLR(-/-) islets) or low cholesterol content (WT islets treated with MβCD) alters both GSIS and Ca(2+) handling. Normalization of cholesterol improves Ca(2+) handling and insulin secretion in LDLR(-/-) islets. Copyright © 2013 Elsevier B.V. All rights reserved.

  19. High saturated fatty acid intake induces insulin secretion by elevating gastric inhibitory polypeptide levels in healthy individuals.

    PubMed

    Itoh, Kazue; Moriguchi, Ririko; Yamada, Yuichiro; Fujita, Misuzu; Yamato, Takako; Oumi, Masayo; Holst, Jens Juul; Seino, Yutaka

    2014-08-01

    Insulin resistance is central to the etiology of the metabolic syndrome cluster of diseases. Evidence suggests that a high-fat diet is associated with insulin resistance, which may be modulated by dietary fatty acid composition. We hypothesized that high saturated fatty acid intake increases insulin and gastric inhibitory polypeptide (GIP) secretion. To clarify the effect of ingested fatty acid composition on glucose levels, we conducted an intervention study to investigate the insulin and plasma GIP responses in 11 healthy women, including a dietary control. Subjects were provided daily control meals (F-20; saturated fatty acids/monounsaturated fatty acids/polyunsaturated fatty acids [S/M/P] ratio, 3:4:3) with 20 energy (E) % fat, followed by 2 isoenergetic experimental meals for 7 days each. These meals comprised 60 E% carbohydrate, 15 E% protein, and 30 E% fat (FB-30; high saturated fatty acid meal; S/M/P, 5:4:1; F-30: reduced saturated fatty acid meal; S/M/P, 3:4:3). On the second day of the F-20 and the last day of F-30 and FB-30, blood samples were taken before and 30, 60, and 120 minutes after a meal tolerance test. The plasma glucose responses did not differ between F-20 and FB-30 or F-30. However, insulin levels were higher after the FB-30 than after the F-20 (P < .01). The GIP response after the FB-30 was higher than that after the F-30 (P < .05). In addition, the difference in the incremental GIP between FB-30 and F-30 correlated significantly and positively with that of the insulin. These results suggest that a high saturated fatty acid content stimulates postprandial insulin release via increased GIP secretion.

  20. Pancreatic Endoderm-Derived From Diabetic Patient-Specific Induced Pluripotent Stem Cell Generates Glucose-Responsive Insulin-Secreting Cells.

    PubMed

    Rajaei, Bahareh; Shamsara, Mehdi; Amirabad, Leila Mohammadi; Massumi, Mohammad; Sanati, Mohammad Hossein

    2017-10-01

    Human-induced pluripotent stem cells (hiPSCs) can potentially serve as an invaluable source for cell replacement therapy and allow the creation of patient- and disease-specific stem cells without the controversial use of embryos and avoids any immunological incompatibility. The generation of insulin-producing pancreatic β-cells from pluripotent stem cells in vitro provides an unprecedented cell source for personal drug discovery and cell transplantation therapy in diabetes. A new five-step protocol was introduced in this study, effectively induced hiPSCs to differentiate into glucose-responsive insulin-producing cells. This process mimics in vivo pancreatic organogenesis by directing cells through stages resembling definitive endoderm, primitive gut-tube endoderm, posterior foregut, pancreatic endoderm, and endocrine precursor. Each stage of differentiation were characterized by stage-specific markers. The produced cells exhibited many properties of functional β-cells, including expression of critical β-cells transcription factors, the potency to secrete C-peptide in response to high levels of glucose and the presence of mature endocrine secretory granules. This high efficient differentiation protocol, established in this study, yielded 79.18% insulin-secreting cells which were responsive to glucose five times higher than the basal level. These hiPSCs-derived glucose-responsive insulin-secreting cells might provide a promising approach for the treatment of type I diabetes mellitus. J. Cell. Physiol. 232: 2616-2625, 2017. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  1. Stimulation of leptin secretion by insulin

    PubMed Central

    Tsai, Minglun; Asakawa, Akihiro; Amitani, Haruka; Inui, Akio

    2012-01-01

    Leptin has a crucial role in regulating food intake and maintaining metabolic homeostasis. Although little is known about the process of leptin secretion, insulin, which has an important role in the metabolism of glucose and lipids, is believed to regulate leptin secretion through a posttranscriptional mechanism in the short term, and via glucose metabolism in the long term. The gastric mucosa secretes leptin, but this mechanism has not been completely elucidated. Understanding the mechanism of insulin-regulated leptin secretion could lead to the development of new treatment methods for obesity and its comorbidities, which are serious public health concerns. PMID:23565488

  2. Dogfish glucagon analogues counter hyperglycaemia and enhance both insulin secretion and action in diet-induced obese diabetic mice.

    PubMed

    O'Harte, F P M; Ng, M T; Lynch, A M; Conlon, J M; Flatt, P R

    2016-10-01

    To investigate the antidiabetic actions of three dogfish glucagon peptide analogues [known glucagon-like peptide-1 and glucagon receptor co-agonists] after chronic administration in diet-induced high-fat-diet-fed diabetic mice. National Institutes of Health Swiss mice were pre-conditioned to a high-fat diet (45% fat) for 100 days, and control mice were fed a normal diet (10% fat). Normal diet control and high-fat-fed control mice received twice-daily intraperitoneal (i.p.) saline injections, while the high-fat-fed treatment groups (n = 8) received twice-daily injections of exendin-4(1-39), [S2a]dogfish glucagon, [S2a]dogfish glucagon exendin-4(31-39) or [S2a]dogfish glucagon-Lys(30) -γ-glutamyl-PAL (25 nmol/kg body weight) for 51 days. After dogfish glucagon analogue treatment, there was a rapid and sustained decrease in non-fasting blood glucose and an associated insulinotropic effect (analysis of variance, p < .05 to <.001) compared with saline-treated high-fat-fed controls. All peptide treatments significantly improved i.p. and oral glucose tolerance with concomitant increased insulin secretion compared with saline-treated high-fat-fed controls (p <.05 to <.001). After chronic treatment, no receptor desensitization was observed but insulin sensitivity was enhanced for all peptide-treated groups (p < .01 to <.001) except [S2a]dogfish glucagon. Both exendin-4 and [S2a]dogfish glucagon exendin-4(31-39) significantly reduced plasma triglyceride concentrations compared with those found in lean controls (p = .0105 and p = .0048, respectively). Pancreatic insulin content was not affected by peptide treatments but [S2a]dogfish glucagon and [S2a]dogfish glucagon exendin-4(31-39) decreased pancreatic glucagon by 28%-34% (p = .0221 and p = .0075, respectively). The percentage of β-cell area within islets was increased by exendin-4 and peptide analogue treatment groups compared with high-fat-fed controls and the β-cell area decreased

  3. Glucose and insulin modify thrombospondin 1 expression and secretion in primary adipocytes from diet-induced obese rats.

    PubMed

    Garcia-Diaz, Diego F; Arellano, Arianna V; Milagro, Fermin I; Moreno-Aliaga, Maria Jesus; Portillo, Maria Puy; Martinez, J Alfredo; Campion, Javier

    2011-09-01

    Thrombospondin 1 (TSP-1), an antiangiogenic factor and transforming growth factor (TGF)-β activity regulator, has been recently recognized as an adipokine that correlates with obesity, inflammation and insulin resistance processes. In the present study, epididymal adipocytes of rats that were fed a chow or a high-fat diet (HFD) for 50 days were isolated and incubated (24-72 h) in low (5.6 mM) or high (HG; 25 mM) glucose, in the presence or absence of 1.6 nM insulin. Rats fed the HF diet showed an established obesity state. Serum TSP-1 levels and TSP-1 mRNA basal expression of adipocytes from HFD rats were higher than those from controls. Adipocytes from HFD animals presented an insulin resistance state, as suggested by the lower insulin-stimulated glucose uptake as compared to controls. TSP-1 expression in culture was higher in adipocytes from obese animals at 24 h, but when the adipocytes were treated with HG, these expression levels dropped dramatically. Later at 72 h, TSP-1 expression was lower in adipocytes from HFD rats, and no effects of the other treatments were observed. Surprisingly, the secretion levels of this protein at 72 h were increased significantly by the HG treatment in both types of adipocytes, although they were even higher in adipocytes from obese animals. Finally, cell viability was significantly reduced by HG treatment in both types of adipocytes. In summary, TSP-1 expression/secretion was modulated in an in vitro model of insulin-resistant adipocytes. The difference between expression and secretion patterns suggests a posttranscriptional regulation. The present study confirms that TPS-1 is closely associated with obesity-related mechanisms.

  4. Evaluation of insulin secretion and action in New World camelids.

    PubMed

    Firshman, Anna M; Cebra, Christopher K; Schanbacher, Barbara J; Seaquist, Elizabeth R

    2013-01-01

    To measure and compare insulin secretion and sensitivity in healthy alpacas and llamas via glucose clamping techniques. 8 llamas and 8 alpacas. Hyperinsulinemic euglycemic clamping (HEC) and hyperglycemic clamping (HGC) were performed on each camelid in a crossover design with a minimum 48-hour washout period between clamping procedures. The HEC technique was performed to measure insulin sensitivity. Insulin was infused IV at 6 mU/min/kg for 4 hours, and an IV infusion of glucose was adjusted to maintain blood glucose concentration at 150 mg/dL. Concentrations of blood glucose and plasma insulin were determined throughout. The HGC technique was performed to assess insulin secretion in response to exogenous glucose infusion. An IV infusion of glucose was administered to maintain blood glucose concentration at 320 mg/dL for 3 hours, and concentrations of blood glucose and plasma insulin were determined throughout. Alpacas and llamas were not significantly different with respect to whole-body insulin sensitivity during HEC or in pancreatic β-cell response during HGC. Alpacas and llamas had markedly lower insulin sensitivity during HEC and markedly lower pancreatic β-cell response during HGC, in comparison with many other species. New World camelids had lower glucose-induced insulin secretion and marked insulin resistance in comparison with other species. This likely contributes to the disorders of fat and glucose metabolism that are common to camelids.

  5. The bile acid sensor FXR regulates insulin transcription and secretion.

    PubMed

    Renga, Barbara; Mencarelli, Andrea; Vavassori, Piero; Brancaleone, Vincenzo; Fiorucci, Stefano

    2010-03-01

    Farnesoid X Receptor plays an important role in maintaining bile acid, cholesterol homeostasis and glucose metabolism. Here we investigated whether FXR is expressed by pancreatic beta-cells and regulates insulin signaling in pancreatic beta-cell line and human islets. We found that FXR activation induces positive regulatory effects on glucose-induced insulin transcription and secretion by genomic and non-genomic activities. Genomic effects of FXR activation relay on the induction of the glucose regulated transcription factor KLF11. Indeed, results from silencing experiments of KLF11 demonstrate that this transcription factor is essential for FXR activity on glucose-induced insulin gene transcription. In addition FXR regulates insulin secretion by non-genomic effects. Thus, activation of FXR in betaTC6 cells increases Akt phosphorylation and translocation of the glucose transporter GLUT2 at plasma membrane, increasing the glucose uptake by these cells. In vivo experiments on Non Obese Diabetic (NOD) mice demonstrated that FXR activation delays development of signs of diabetes, hyperglycemia and glycosuria, by enhancing insulin secretion and by stimulating glucose uptake by the liver. These data established that an FXR-KLF11 regulated pathway has an essential role in the regulation of insulin transcription and secretion induced by glucose.

  6. Milrinone efficiently potentiates insulin secretion induced by orally but not intravenously administered glucose in C57BL6J mice.

    PubMed

    Degerman, Eva; Manganiello, Vincent; Holst, Jens J; Ahrén, Bo

    2004-09-13

    To study the effect of phosphodiesterase (PDE) 3 inhibition on plasma insulin and glucose levels, the selective PDE 3 inhibitor milrinone (0.25, 1.0, and 2.5 mg/kg) was given orally to anesthetized CL57Bl/6J mice 10 min before a gastric glucose gavage (150 mg/mouse). It was found that milrinone augmented the glucose-mediated increase in plasma insulin at 1.0 and 2.5 mg/kg without, however, any improvement in glucose elimination. In contrast, when given 10 min before intravenous glucose (1 g/kg), milrinone (1 mg/kg) did not affect the insulin response to glucose. The increase in glucagon-like peptide-1 (GLP-1) levels after gastric glucose was not altered by milrinone. However, the PDE3 inhibitor augmented the insulin response to intravenous GLP-1 (2.8 nmol/kg). We therefore conclude that PDE3 inhibition by milrinone augments insulin secretion in vivo in mice after oral but not after intravenous glucose, which may be explained by enhanced response to the cAMP-dependent insulinotropic action of endogenously released GLP-1.

  7. Simultaneous measurement of insulin sensitivity, insulin secretion and the disposition index in conscious unhandled mice

    PubMed Central

    Alonso, L. C.; Watanabe, Y.; Stefanovski, D.; Lee, E. J.; Singamsetty, S.; Romano, L. C.; Zou, B.; Garcia-Ocana, A.; Bergman, R. N.; O’Donnell, C. P.

    2012-01-01

    Of the parameters that determine glucose disposal and progression to diabetes in humans: first-phase insulin secretion, glucose effectiveness, insulin sensitivity, and the disposition index, only insulin sensitivity can be reliably measured in conscious mice. To determine the importance of the other parameters in murine glucose homeostasis in lean and obese states, we developed the frequently sampled intravenous glucose tolerance test (FSIVGTT) for use in unhandled mice. We validated the conscious FSIVGTT against the euglycemic clamp for measuring insulin sensitivity in lean and obese mice. Insulin resistant mice had increased first-phase insulin secretion, decreased glucose effectiveness and a reduced disposition index, qualitatively similar to humans. Intriguingly, while insulin secretion explained most of the variation in glucose disposal in lean mice, glucose effectiveness and the disposition index more strongly predicted glucose disposal in obese mice. Disposition index curves identified individual diet-induced obese mice as having compensated or decompensated insulin secretion. Conscious FSIVGTT opens the door to apply mouse genetics to the determinants of in vivo insulin secretion, glucose effectiveness and disposition index, and further validates the mouse as a model of metabolic disease. PMID:22331130

  8. High heritability and genetic correlation of intravenous glucose- and tolbutamide-induced insulin secretion among non-diabetic family members of type 2 diabetic patients.

    PubMed

    Gjesing, Anette P; Hornbak, Malene; Allin, Kristine H; Ekstrøm, Claus T; Urhammer, Søren A; Eiberg, Hans; Pedersen, Oluf; Hansen, Torben

    2014-06-01

    The aim of this study was to estimate the heritability of quantitative measures of glucose regulation obtained from a tolbutamide-modified frequently sampled IVGTT (t-FSIGT) and to correlate the heritability of the glucose-stimulated beta cell response to the tolbutamide-induced beta cell response. In addition, single nucleotide polymorphisms (SNPs) having an exclusive effect on either glucose- or tolbutamide-stimulated insulin release were identified. Two hundred and eighty-four non-diabetic family members of patients with type 2 diabetes underwent a t-FSIGT with intravenous injection of glucose at t = 0 min and tolbutamide at t = 20 min. Measurements of plasma glucose, serum insulin and serum C-peptide were taken at 33 time points from fasting to 180 min. Insulin secretion rate, acute insulin response (AIR), disposition index (DI) after glucose and disposition index after tolbutamide (DIT), insulin sensitivity (SI), glucose effectiveness (SG) and beta cell responsiveness to glucose were calculated. A polygenic variance component model was used to estimate heritability, genetic correlations and associations. We found high heritabilities for acute insulin secretion subsequent to glucose stimulation (AIRglucose h (2) ± SE: 0.88 ± 0.14), but these were slightly lower after tolbutamide (AIRtolbutamide h (2) ± SE: 0.69 ± 0.14). We also estimated the heritabilities for SI (h (2) ± SE: 0.26 ± 0.12), SG (h (2) ± SE: 0.47 ± 0.13), DI (h (2) ± SE: 0.56 ± 0.14), DIT (h (2) ± SE: 0.49 ± 0.14) and beta cell responsiveness to glucose (h (2) ± SE: 0.66 ± 0.12). Additionally, strong genetic correlations were found between measures of beta cell response after glucose and tolbutamide stimulation, with correlation coefficients ranging from 0.77 to 0.88. Furthermore, we identified five SNPs with an exclusive effect on either glucose-stimulated (rs5215, rs1111875, rs11920090) or tolbutamide-stimulated (rs

  9. Insulin secretion after injuries of differing severity in the rat.

    PubMed Central

    Frayn, K. N.

    1976-01-01

    The effects on insulin secretion of injuries of differing severity have been studied in the rat. The injuries used were dorsal scalds to 20% and 40% of the body surface area, and a 4-h period of bilateral hind-limb ischaemia. These injuries resulted in 48 h mortality rates of 0/10, 7/10 and 5/10 respectively. Rats were studied 1-5-2 h after scalding or removal of tourniquets. The blood glucose concentration was markedly raised after all these injuries, and the plasma insulin concentration was also raised, so that the insulin to glucose ratio in any group did not differ significantly from that in non-injured controls. Injection of glucose (0-5 g/kg i.v.) induced a rise in insulin concentration in all groups, although the insulin to glucose ratio after the lethal 40% scald was lower than in control rats. It was concluded that in the rat normal insulin secretion is maintained even after lethal injuries, although some suppression of the insulin response to exogenous glucose may occur. Insulin resistance is more important in the rat than impairment of insulin secretion even at an early stage after injury. PMID:782499

  10. A mathematical model of insulin secretion.

    PubMed

    Shannon, A G; Hogg, J M; Ollerton, R L; Luzio, S; Owens, D R

    1994-01-01

    Diabetes mellitus is a chronic state of excessive blood glucose levels (hyperglycaemia), which may result from many environmental and genetic factors, often acting jointly. The major regulator of glucose concentration in the blood is insulin. It is known that about 50% of the insulin is taken up by the liver on passing through it after secretion from the pancreas. The precise value of this fractional uptake is not known, so the prehepatic insulin secretion rates cannot be readily estimated from the plasma insulin concentration levels. By utilizing the equimolar secretion of insulin and connecting peptide (C-peptide) from the pancreas, a noninvasive method has been formulated. This was based on a compartmental model which involved the pancreas, liver, and plasma. The resulting differential equation yielded a gamma variate solution which could be readily linearized. The model was then tested on 56 normal (51 nonobese and 5 obese) subjects, and three groups of subjects with diabetes who could be labelled as mild, moderate, and severe (based on the fasting plasma glucose concentration) with 83, 88, and 64 subjects respectively. We have focused on the human patient environment of the clinician to produce a distinct model which gave a consistent pattern within all four groups with good fits between observed and theoretical values of the plasma insulin levels. The consequent rates for insulin secretion were consistent across the groups and were clinically meaningful.

  11. [Prostaglandins, insulin secretion and diabetes mellitus].

    PubMed

    Giugliano, D; Torella, R; Scheen, A J; Lefebvre, P J; D'Onofrio, F

    1988-12-01

    The islets of Langerhans have the enzymatic equipment permitting the synthesis of the metabolites of arachidonic acid: cyclo-oxygenase and lipo-oxygenase. Numerous studies have shown that cyclo-oxygenase derivatives, mainly PGE2, reduce the insulin response to glucose whereas lipo-oxygenase derivatives, mainly 15-HPETE, stimulate insulin secretion. So, for instance, drugs that increase prostaglandins synthesis as colchicine or furosemide inhibit insulin secretion while non steroid anti-inflammator drugs, mainly salicylates, which inhibit cyclo-oxygenase, enhance the insulin response to various stimuli. In type-2 (non insulin-dependent) diabetes, an increased sensitivity to endogenous prostaglandins has been proposed as a possible cause for the insulin secretion defect which characterizes this disease. Play in favor of this hypothesis the fact that the administration of PGE inhibits the insulin response to arginine in type-2 diabetics but not in normal subject and the fact that the administration of salicylates could improve the insulin response to glucose in some of these patients.

  12. New insights concerning insulin synthesis and its secretion in rat hippocampus and cerebral cortex: amyloid-β1-42-induced reduction of proinsulin level via glycogen synthase kinase-3β.

    PubMed

    Nemoto, Takayuki; Toyoshima-Aoyama, Fumiyo; Yanagita, Toshihiko; Maruta, Toyoaki; Fujita, Hiroshi; Koshida, Tomohiro; Yonaha, Tetsu; Wada, Akihiko; Sawaguchi, Akira; Murakami, Manabu

    2014-02-01

    The reduction of insulin levels in hippocampal areas is associated with Alzheimer's disease. The present study using rat brain explores the mechanisms of insulin synthesis and secretion, as well as amyloid-β1-42 (Aβ(1-42))-induced reduction of proinsulin expression. After confirming the expression of insulin mRNA and proinsulin in rat brain, we visualized and analyzed the motion of insulin secretion in rat hippocampal neurons using pH-sensitive green fluorescent protein (pHluorin) fused to the insulin. In the rat hippocampal neurons expressing insulin-pHluorin, time-lapse confocal laser scanning microscopy revealed the appearance of fluorescent spots induced by depolarization after stimulation with 50 mM KCl. In these fluorescent spots, Ca(2+)-dependent activator protein for secretion 2 (CAPS2), which is the regulator of the dense-core vesicle involving neuronal peptides, was co-localized with insulin-pHluorin. However, Aβ(1-42)-induced reduction of proinsulin in rat hippocampal neurons was inhibited by treatment with lithium and transfection with glycogen synthase kinase-3β (GSK-3β) siRNA. These results demonstrate that synthesized insulin is secreted from rat hippocampal and cortical neuron's dense-core vesicles, and that activation of GSK-3β in Aβ(1-42)-induced Alzheimer's model hippocampal neurons decreases the insulin synthesis.

  13. Deletion of GPR40 Impairs Glucose-Induced Insulin Secretion In Vivo in Mice Without Affecting Intracellular Fuel Metabolism in Islets

    SciTech Connect

    Alquier, Thierry; Peyot, Marie-Line; Latour, M. G.; Kebede, Melkam; Sorensen, Christina M.; Gesta, Stephane; Kahn, C. R.; Smith, Richard D.; Jetton, Thomas L.; Metz, Thomas O.; Prentki, Marc; Poitout, Vincent J.

    2009-11-01

    The G protein-coupled receptor GPR40 mediates fatty-acid potentiation of glucose-stimulated insulin secretion, but its contribution to insulin secretion in vivo and mechanisms of action remain uncertain. This study was aimed to ascertain whether GPR40 controls insulin secretion in vivo and modulates intracellular fuel metabolism in islets. We observed that glucose- and arginine-stimulated insulin secretion, assessed by hyperglycemic clamps, was decreased by approximately 60% in GPR40 knock-out (KO) fasted and fed mice, without changes in insulin sensitivity assessed by hyperinsulinemic-euglycemic clamps. Glucose and palmitate metabolism were not affected by GPR40 deletion. Lipid profiling revealed a similar increase in triglyceride and decrease in lysophosphatidylethanolamine species in WT and KO islets in response to palmitate. These results demonstrate that GPR40 regulates insulin secretion in vivo not only in response to fatty acids but also to glucose and arginine, without altering intracellular fuel metabolism.

  14. Insulin reciprocally regulates glucagon secretion in humans.

    PubMed

    Cooperberg, Benjamin A; Cryer, Philip E

    2010-11-01

    We tested the hypothesis that an increase in insulin per se, i.e., in the absence of zinc, suppresses glucagon secretion during euglycemia and that a decrease in insulin per se stimulates glucagon secretion during hypoglycemia in humans. We measured plasma glucagon concentrations in patients with type 1 diabetes infused with the zinc-free insulin glulisine on three occasions. Glulisine was infused with clamped euglycemia (∼95 mg/dl [5.3 mmol/l]) from 0 to 60 min on all three occasions. Then, glulisine was discontinued with clamped euglycemia or with clamped hypoglycemia (∼55 mg/dl [3.0 mmol/l]) or continued with clamped hypoglycemia from 60 to 180 min. Plasma glucagon concentrations were suppressed by -13 ± 3, -9 ± 3, and -12 ± 2 pg/ml (-3.7 ± 0.9, -2.6 ± 0.9, and -3.4 ± 0.6 pmol/l), respectively, (all P < 0.01) during zinc-free hyperinsulinemic euglycemia over the first 60 min. Glucagon levels remained suppressed following a decrease in zinc-free insulin with euglycemia (-14 ± 3 pg/ml [-4.0 ± 0.9 pmol/l]) and during sustained hyperinsulinemia with hypoglycemia (-14 ± 2 pg/ml [-4.0 ± 0.6 pmol/l]) but increased to -3 ± 3 pg/ml (-0.9 ± 0.9 pmol/l) (P < 0.01) following a decrease in zinc-free insulin with hypoglycemia over the next 120 min. These data indicate that an increase in insulin per se suppresses glucagon secretion and a decrease in insulin per se, in concert with a low glucose concentration, stimulates glucagon secretion. Thus, they document that insulin is a β-cell secretory product that, in concert with glucose and among other signals, reciprocally regulates α-cell glucagon secretion in humans.

  15. Metformin Ameliorates Dysfunctional Traits of Glibenclamide- and Glucose-Induced Insulin Secretion by Suppression of Imposed Overactivity of the Islet Nitric Oxide Synthase-NO System.

    PubMed

    Lundquist, Ingmar; Mohammed Al-Amily, Israa; Meidute Abaraviciene, Sandra; Salehi, Albert

    2016-01-01

    Metformin lowers diabetic blood glucose primarily by reducing hepatic gluconeogenesis and increasing peripheral glucose uptake. However, possible effects by metformin on beta-cell function are incompletely understood. We speculated that metformin might positively influence insulin secretion through impacting the beta-cell nitric oxide synthase (NOS)-NO system, a negative modulator of glucose-stimulated insulin release. In short-time incubations with isolated murine islets either glibenclamide or high glucose augmented insulin release associated with increased NO production from both neural and inducible NOS. Metformin addition suppressed the augmented NO generation coinciding with amplified insulin release. Islet culturing with glibenclamide or high glucose revealed pronounced fluorescence of inducible NOS in the beta-cells being abolished by metformin co-culturing. These findings were reflected in medium nitrite-nitrate levels. A glucose challenge following islet culturing with glibenclamide or high glucose revealed markedly impaired insulin response. Metformin co-culturing restored this response. Culturing murine islets and human islets from controls and type 2 diabetics with high glucose or high glucose + glibenclamide induced a pronounced decrease of cell viability being remarkably restored by metformin co-culturing. We show here, that imposed overactivity of the beta-cell NOS-NO system by glibenclamide or high glucose leads to insulin secretory dysfunction and reduced cell viability and also, importantly, that these effects are relieved by metformin inhibiting beta-cell NO overproduction from both neural and inducible NOS thus ameliorating a concealed negative influence by NO induced by sulfonylurea treatment and/or high glucose levels. This double-edged effect of glibenclamide on the beta-cellsuggests sulfonylurea monotherapy in type 2 diabetes being avoided.

  16. Metformin Ameliorates Dysfunctional Traits of Glibenclamide- and Glucose-Induced Insulin Secretion by Suppression of Imposed Overactivity of the Islet Nitric Oxide Synthase-NO System

    PubMed Central

    Lundquist, Ingmar; Mohammed Al-Amily, Israa; Meidute Abaraviciene, Sandra

    2016-01-01

    Metformin lowers diabetic blood glucose primarily by reducing hepatic gluconeogenesis and increasing peripheral glucose uptake. However, possible effects by metformin on beta-cell function are incompletely understood. We speculated that metformin might positively influence insulin secretion through impacting the beta-cell nitric oxide synthase (NOS)-NO system, a negative modulator of glucose-stimulated insulin release. In short-time incubations with isolated murine islets either glibenclamide or high glucose augmented insulin release associated with increased NO production from both neural and inducible NOS. Metformin addition suppressed the augmented NO generation coinciding with amplified insulin release. Islet culturing with glibenclamide or high glucose revealed pronounced fluorescence of inducible NOS in the beta-cells being abolished by metformin co-culturing. These findings were reflected in medium nitrite-nitrate levels. A glucose challenge following islet culturing with glibenclamide or high glucose revealed markedly impaired insulin response. Metformin co-culturing restored this response. Culturing murine islets and human islets from controls and type 2 diabetics with high glucose or high glucose + glibenclamide induced a pronounced decrease of cell viability being remarkably restored by metformin co-culturing. We show here, that imposed overactivity of the beta-cell NOS-NO system by glibenclamide or high glucose leads to insulin secretory dysfunction and reduced cell viability and also, importantly, that these effects are relieved by metformin inhibiting beta-cell NO overproduction from both neural and inducible NOS thus ameliorating a concealed negative influence by NO induced by sulfonylurea treatment and/or high glucose levels. This double-edged effect of glibenclamide on the beta-cellsuggests sulfonylurea monotherapy in type 2 diabetes being avoided. PMID:27820841

  17. THE HYPOPHYSIS AND SECRETION OF INSULIN

    PubMed Central

    Houssay, B. A.; Foglia, V. G.; Smyth, F. S.; Rietti, C. T.; Houssay, A. B.

    1942-01-01

    The ability of the pancreas, from various types of dogs, to correct diabetic hyperglycemia has been studied (Table XI). The pancreas from one animal was united by a vascular union with the neck blood vessels of another dog which had been pancreatectomized for 20 hours. The time necessary to reduce the blood sugar level to 120 mg. per cent was determined. 1. Pancreas from 6 hypophysectomized dogs produced a normal insulin secretion, showing that an anterior pituitary hormone is not necessary for its production or maintenance. 2. In 14 of 17 normal dogs given anterior pituitary extract for 3 or more consecutive days and presenting diabetes (fasting blood sugar 150 mg. per cent or more) the pancreas showed diminished insulin production. 3. In animals which remained diabetic after discontinuing the injections of hypophyseal extract, the pancreas islands were markedly pathologic and the insulin secretion was practically nil. 4. When hyperglycemia existed on the 2nd to 5th day but fell later, the insulin secretion of 5 dogs was normal in 2, supernormal in 1, and less than normal in 2. Histologic examination showed a restoration of beta cells. 5. In 14 dogs resistant to the diabetogenic action of anterior pituitary extract, as shown by little or no change in blood sugar, the pancreatic secretion of insulin was normal in 6 cases, supernormal in 3, and subnormal in 5 cases. Clear signs of hyperfunction of B cells were observed. In 6 resistant animals a high blood sugar (150 mg. per cent) appeared shortly before transplanting, but insulin secretion was normal in 4, supernormal in 1, and subnormal in 1 case. 6. With one injection of extract and 1 day of hyperglycemia the capacity of the pancreas to secrete insulin was not altered. 7. A high blood sugar level lasting 4 days does not alter the islets. The hypophyseal extract acts, therefore, by some other mechanism. In normal dogs, the continuous intravenous infusion of glucose for 4 days maintained the blood sugar at levels as

  18. The stimulus-secretion coupling of glucose-induced insulin release XIX. The insulinotropic effect of glyceraldehyde.

    PubMed

    Malaisse, W J; Herchuelz, A; Levy, J; Sener, A; Pipeleers, D G; Devis, G; Somers, G; Obberghen, E V

    Glyceraldehyde is known to stimulate insulin release. Its influence on various parameters of islet function was investigated in order to assess the possible significance of glycolsis in the insulinotropic action of glucose. In the absence of glucose, glyceraldehyde (5-20 mM), but neither dihydroxyacetone nor glycerol stimulated insulin release in rat isolated islets. The glucose-like effect glyceraldehyde (10 mM) was characterized by a shift to the left of the curve relating insulin release to glucose concentration, without any significant increase in the maximal velocity of the secretory process. In the isolated perfused rat pancreas, glyceraldehyde provoked a biphasic secretory response. Glyceraldehyde-induced insulin release was inhibited in the absence of calcium or in the presence of epinephrine, unaffected by mannoheptulose or 3,3-tetramethyleneglutaric acid, and enhanced by theophylline and cytochalism B. Glyceraldehyde also stimulated to pro-insulin biosynthesis and 45Ca net uptake by isolated islets, the latter effect being apparently due, in part at least, to inhibition of calcium outward transport across the cell membrane. At concentrations of nearly equivalent insulinotropic potency, glucose and glyceraldehyde were metabolized at rates yielding comparable output of both lactate and 14CO2. The data indicate that glyceraldehyde mimics many effects of glucose on islet function, suggesting that the insulinotropic action of glucose may be related to its metabolism through the glycolytic pathway.

  19. Nutrient regulation of insulin secretion and action.

    PubMed

    Newsholme, Philip; Cruzat, Vinicius; Arfuso, Frank; Keane, Kevin

    2014-06-01

    Pancreatic β-cell function is of critical importance in the regulation of fuel homoeostasis, and metabolic dysregulation is a hallmark of diabetes mellitus (DM). The β-cell is an intricately designed cell type that couples metabolism of dietary sources of carbohydrates, amino acids and lipids to insulin secretory mechanisms, such that insulin release occurs at appropriate times to ensure efficient nutrient uptake and storage by target tissues. However, chronic exposure to high nutrient concentrations results in altered metabolism that impacts negatively on insulin exocytosis, insulin action and may ultimately lead to development of DM. Reduced action of insulin in target tissues is associated with impairment of insulin signalling and contributes to insulin resistance (IR), a condition often associated with obesity and a major risk factor for DM. The altered metabolism of nutrients by insulin-sensitive target tissues (muscle, adipose tissue and liver) can result in high circulating levels of glucose and various lipids, which further impact on pancreatic β-cell function, IR and progression of the metabolic syndrome. Here, we have considered the role played by the major nutrient groups, carbohydrates, amino acids and lipids, in mediating β-cell insulin secretion, while also exploring the interplay between amino acids and insulin action in muscle. We also focus on the effects of altered lipid metabolism in adipose tissue and liver resulting from activation of inflammatory processes commonly observed in DM pathophysiology. The aim of this review is to describe commonalities and differences in metabolism related to insulin secretion and action, pertinent to the development of DM. © 2014 Society for Endocrinology.

  20. Nypa fruticans Wurmb. Vinegar's Aqueous Extract Stimulates Insulin Secretion and Exerts Hepatoprotective Effect on STZ-Induced Diabetic Rats.

    PubMed

    Yusoff, Nor Adlin; Lim, Vuanghao; Al-Hindi, Bassel; Abdul Razak, Khairul Niza; Widyawati, Tri; Anggraini, Dwi Rita; Ahmad, Mariam; Asmawi, Mohd Zaini

    2017-08-23

    An aqueous extract (AE) of vinegar made from Nypa fruticans Wurmb. can improve postprandial glucose levels in normoglycaemic rats. The aim of this study was to evaluate its antihyperglycaemic activity further using in vivo and in vitro approaches. AE was administered to streptozotocin (STZ)-induced diabetic rats twice daily at three doses (1000, 500, and 250 mg/kg b.w.) for 12 days p.o. Several biochemical analyses and a histological study of the pancreas and liver were performed, accompanied by a cell culture assay. As compared to diabetic control (DC), AE at the doses of 500 and 1000 mg/kg b.w. caused significant reduction (p < 0.05) of blood glucose, total cholesterol and triglycerides levels, with positive improvement of serum insulin levels. Interestingly, immunohistochemical staining of the pancreas suggested no β-cell regeneration, despite significant increase in insulin production. AE-treated groups, however, showed overall restoration of the hepatic histoarchitecture of STZ-induced liver damage, suggesting a possible hepatoprotective effect. The pancreatic effect of AE was further studied through RIN-5F cell culture, which revealed a positive stimulatory effect on insulin release at a basal glucose concentration (1.1 mM). Nypa fruticans Wurmb. vinegar's aqueous extract exerts its antihyperglycaemic activity, at least in part, through insulin stimulatory and hepatoprotective effects.

  1. Self-inducible secretion of glucagon-like peptide-1 (GLP-1) that allows MIN6 cells to maintain insulin secretion and insure cell survival.

    PubMed

    Nakashima, Koji; Shimoda, Masashi; Hamamoto, Sumiko; Tatsumi, Fuminori; Hirukawa, Hidenori; Tawaramoto, Kazuhito; Kanda, Yukiko; Kaku, Kohei

    2012-02-26

    Based on the hypothesis that MIN6 cells could produce glucagon-like peptide-1 (GLP-1) to maintain cell survival, we analyzed the effects of GLP-1 receptor agonist, exendin-4 (Ex4), and antagonist, exendin-(9-39) (Ex9) on cell function and cell differentiation. MIN6 cells expressed proglucagon mRNAs and produced GLP-1, which was accelerated by Ex4 and suppressed by Ex9. Moreover, Ex4 further enhanced glucose-stimulated GLP-1 secretion, suggesting autocrine loop-contributed amplification of the GLP-1 signal. Ex4 up-regulated cell differentiation- and cell function-related CREBBP, Pdx-1, Pax6, proglucagon, and PC1/3 gene expressions. The confocal laser scanning images revealed that GLP-1 positive cells were dominant in the early stage of cells, but positive for insulin were more prominent in the mature stage of cells. Ex4 accelerated cell viability, while Ex9 and anti-GLP-1 receptor antibody enhanced cell apoptosis. MIN6 cells possess a mechanism of GLP-1 signal amplification in an autocrine fashion, by which the cells maintained insulin production and cell survival.

  2. Insulin secretion in health and disease: nutrients dictate the pace.

    PubMed

    Regazzi, Romano; Rodriguez-Trejo, Adriana; Jacovetti, Cécile

    2016-02-01

    Insulin is a key hormone controlling metabolic homeostasis. Loss or dysfunction of pancreatic β-cells lead to the release of insufficient insulin to cover the organism needs, promoting diabetes development. Since dietary nutrients influence the activity of β-cells, their inadequate intake, absorption and/or utilisation can be detrimental. This review will highlight the physiological and pathological effects of nutrients on insulin secretion and discuss the underlying mechanisms. Glucose uptake and metabolism in β-cells trigger insulin secretion. This effect of glucose is potentiated by amino acids and fatty acids, as well as by entero-endocrine hormones and neuropeptides released by the digestive tract in response to nutrients. Glucose controls also basal and compensatory β-cell proliferation and, along with fatty acids, regulates insulin biosynthesis. If in the short-term nutrients promote β-cell activities, chronic exposure to nutrients can be detrimental to β-cells and causes reduced insulin transcription, increased basal secretion and impaired insulin release in response to stimulatory glucose concentrations, with a consequent increase in diabetes risk. Likewise, suboptimal early-life nutrition (e.g. parental high-fat or low-protein diet) causes altered β-cell mass and function in adulthood. The mechanisms mediating nutrient-induced β-cell dysfunction include transcriptional, post-transcriptional and translational modifications of genes involved in insulin biosynthesis and secretion, carbohydrate and lipid metabolism, cell differentiation, proliferation and survival. Altered expression of these genes is partly caused by changes in non-coding RNA transcripts induced by unbalanced nutrient uptake. A better understanding of the mechanisms leading to β-cell dysfunction will be critical to improve treatment and find a cure for diabetes.

  3. Redox Signal-mediated Enhancement of the Temperature Sensitivity of Transient Receptor Potential Melastatin 2 (TRPM2) Elevates Glucose-induced Insulin Secretion from Pancreatic Islets.

    PubMed

    Kashio, Makiko; Tominaga, Makoto

    2015-05-08

    Transient receptor potential melastatin 2 (TRPM2) is a thermosensitive Ca(2+)-permeable cation channel expressed by pancreatic β cells where channel function is constantly affected by body temperature. We focused on the physiological functions of redox signal-mediated TRPM2 activity at body temperature. H2O2, an important molecule in redox signaling, reduced the temperature threshold for TRPM2 activation in pancreatic β cells of WT mice but not in TRPM2KO cells. TRPM2-mediated [Ca(2+)]i increases were likely caused by Ca(2+) influx through the plasma membrane because the responses were abolished in the absence of extracellular Ca(2+). In addition, TRPM2 activation downstream from the redox signal plus glucose stimulation enhanced glucose-induced insulin secretion. H2O2 application at 37 °C induced [Ca(2+)]i increases not only in WT but also in TRPM2KO β cells. This was likely due to the effect of H2O2 on KATP channel activity. However, the N-acetylcysteine-sensitive fraction of insulin secretion by WT islets was increased by temperature elevation, and this temperature-dependent enhancement was diminished significantly in TRPM2KO islets. These data suggest that endogenous redox signals in pancreatic β cells elevate insulin secretion via TRPM2 sensitization and activity at body temperature. The results in this study could provide new therapeutic approaches for the regulation of diabetic conditions by focusing on the physiological function of TRPM2 and redox signals. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  4. Chronic DPP-IV inhibition with PKF-275-055 attenuates inflammation and improves gene expressions responsible for insulin secretion in streptozotocin induced diabetic rats.

    PubMed

    Akarte, Atul Sureshrao; Srinivasan, B P; Gandhi, Sonia; Sole, Sushant

    2012-09-29

    Inhibitors of dipeptidyl peptidase-4 (DPP-IV), a key regulator of the actions of incretin hormones, exert antihyperglycemic effects in type 2 diabetic patients. A major question concerns the potential ability of long term DPP-IV inhibition to have beneficial disease-modifying effects, specifically to attenuate loss of pancreatic β-cell mass due to oxidative stress induced inflammation. Here, we investigated the effects of a potent and selective DPP-4 inhibitor, an analog of vildagliptin (PKF-275-055), on glycemic control, pancreatic β-cell mass, genes and proteins expressions, tumor necrosis factor-alpha, and nitric oxide in an n2-STZ diabetic model of rat with defects in insulin sensitivity and secretion. To induce NIDDM, streptozotocin (STZ) 90 mg/kg was administered i.p. to a group of 2 days old pups. Diabetic rats were administered orally with vildagliptin analog PKF-275-055. Saline treated animals served as diabetic control. Significant and dose-dependent correction of postprandial hyperglycemia was observed in diabetic rats following 8 weeks of chronic therapy. Treatment with PKF-275-055 showed increased the number of insulin-positive β-cells in islets and improved the expressions of genes and proteins are responsible for insulin secretions. In addition, treatment of rats with PKF-275-055 significantly increased insulin content, glycogen content and total proteins content; and decreased the inflammatory markers i.e. nitric oxide and TNF-alpha. The present studies indicate that PKF-275-055 is a novel selective DPP-IV inhibitor having potential to reduce inflammation that might be a potential agent for type 2 diabetes.

  5. Effects of glucosamine infusion on insulin secretion and insulin action in humans.

    PubMed

    Monauni, T; Zenti, M G; Cretti, A; Daniels, M C; Targher, G; Caruso, B; Caputo, M; McClain, D; Del Prato, S; Giaccari, A; Muggeo, M; Bonora, E; Bonadonna, R C

    2000-06-01

    Glucose toxicity (i.e., glucose-induced reduction in insulin secretion and action) may be mediated by an increased flux through the hexosamine-phosphate pathway. Glucosamine (GlcN) is widely used to accelerate the hexosamine pathway flux, independently of glucose. We tested the hypothesis that GlcN can affect insulin secretion and/or action in humans. In 10 healthy subjects, we sequentially performed an intravenous glucose (plus [2-3H]glucose) tolerance test (IVGTT) and a euglycemic insulin clamp during either a saline infusion or a low (1.6 micromol x min(-1) x kg(-1)) or high (5 micromol x min(-1) x kg(-1) [n = 5]) GlcN infusion. Beta-cell secretion, insulin (SI*-IVGTT), and glucose (SG*) action on glucose utilization during the IVGTT were measured according to minimal models of insulin secretion and action. Infusion of GlcN did not affect readily releasable insulin levels, glucose-stimulated insulin secretion (GSIS), or the time constant of secretion, but it increased both the glucose threshold of GSIS (delta approximately 0.5-0.8 mmol/l, P < 0.03-0.01) and plasma fasting glucose levels (delta approximately 0.3-0.5 mmol/l, P < 0.05-0.02). GlcN did not change glucose utilization or intracellular metabolism (glucose oxidation and glucose storage were measured by indirect calorimetry) during the clamp. However, high levels of GlcN caused a decrease in SI*-IVGTT (delta approximately 30%, P < 0.02) and in SG* (delta approximately 40%, P < 0.05). Thus, in humans, acute GlcN infusion recapitulates some metabolic features of human diabetes. It remains to be determined whether acceleration of the hexosamine pathway can cause insulin resistance at euglycemia in humans.

  6. Insulin secretion and sensitivity in space flight: diabetogenic effects

    NASA Technical Reports Server (NTRS)

    Tobin, Brian W.; Uchakin, Peter N.; Leeper-Woodford, Sandra K.

    2002-01-01

    Nearly three decades of space flight research have suggested that there are subclinical diabetogenic changes that occur in microgravity. Alterations in insulin secretion, insulin sensitivity, glucose tolerance, and metabolism of protein and amino acids support the hypothesis that insulin plays an essential role in the maintenance of muscle mass in extended-duration space flight. Experiments in flight and after flight and ground-based bedrest studies have associated microgravity and its experimental paradigms with manifestations similar to those of diabetes, physical inactivity, and aging. We propose that these manifestations are characterized best by an etiology that falls into the clinical category of "other" causes of diabetes, including, but not restricted to, genetic beta-cell defects, insulin action defects, diseases of the endocrine pancreas, endocrinopathies, drug or chemically induced diabetes, infections, immune-mediated metabolic alteration, and a host of genetic related diseases. We present data showing alterations in tumor necrosis factor-alpha production, insulin secretion, and amino acid metabolism in pancreatic islets of Langerhans cultured in a ground-based cell culture bioreactor that mimics some of the effects of microgravity. Taken together, space flight research, ground-based studies, and bioreactor studies of pancreatic islets of Langerhans support the hypothesis that the pancreas is unable to overcome peripheral insulin resistance and amino acid dysregulation during space flight. We propose that measures of insulin secretion and insulin action will be necessary to design effective countermeasures against muscle loss, and we advance the "disposition index" as an essential model to be used in the clinical management of space flight-induced muscle loss.

  7. Insulin secretion and sensitivity in space flight: diabetogenic effects

    NASA Technical Reports Server (NTRS)

    Tobin, Brian W.; Uchakin, Peter N.; Leeper-Woodford, Sandra K.

    2002-01-01

    Nearly three decades of space flight research have suggested that there are subclinical diabetogenic changes that occur in microgravity. Alterations in insulin secretion, insulin sensitivity, glucose tolerance, and metabolism of protein and amino acids support the hypothesis that insulin plays an essential role in the maintenance of muscle mass in extended-duration space flight. Experiments in flight and after flight and ground-based bedrest studies have associated microgravity and its experimental paradigms with manifestations similar to those of diabetes, physical inactivity, and aging. We propose that these manifestations are characterized best by an etiology that falls into the clinical category of "other" causes of diabetes, including, but not restricted to, genetic beta-cell defects, insulin action defects, diseases of the endocrine pancreas, endocrinopathies, drug or chemically induced diabetes, infections, immune-mediated metabolic alteration, and a host of genetic related diseases. We present data showing alterations in tumor necrosis factor-alpha production, insulin secretion, and amino acid metabolism in pancreatic islets of Langerhans cultured in a ground-based cell culture bioreactor that mimics some of the effects of microgravity. Taken together, space flight research, ground-based studies, and bioreactor studies of pancreatic islets of Langerhans support the hypothesis that the pancreas is unable to overcome peripheral insulin resistance and amino acid dysregulation during space flight. We propose that measures of insulin secretion and insulin action will be necessary to design effective countermeasures against muscle loss, and we advance the "disposition index" as an essential model to be used in the clinical management of space flight-induced muscle loss.

  8. Insulin secretion and sensitivity in space flight: diabetogenic effects.

    PubMed

    Tobin, Brian W; Uchakin, Peter N; Leeper-Woodford, Sandra K

    2002-10-01

    Nearly three decades of space flight research have suggested that there are subclinical diabetogenic changes that occur in microgravity. Alterations in insulin secretion, insulin sensitivity, glucose tolerance, and metabolism of protein and amino acids support the hypothesis that insulin plays an essential role in the maintenance of muscle mass in extended-duration space flight. Experiments in flight and after flight and ground-based bedrest studies have associated microgravity and its experimental paradigms with manifestations similar to those of diabetes, physical inactivity, and aging. We propose that these manifestations are characterized best by an etiology that falls into the clinical category of "other" causes of diabetes, including, but not restricted to, genetic beta-cell defects, insulin action defects, diseases of the endocrine pancreas, endocrinopathies, drug or chemically induced diabetes, infections, immune-mediated metabolic alteration, and a host of genetic related diseases. We present data showing alterations in tumor necrosis factor-alpha production, insulin secretion, and amino acid metabolism in pancreatic islets of Langerhans cultured in a ground-based cell culture bioreactor that mimics some of the effects of microgravity. Taken together, space flight research, ground-based studies, and bioreactor studies of pancreatic islets of Langerhans support the hypothesis that the pancreas is unable to overcome peripheral insulin resistance and amino acid dysregulation during space flight. We propose that measures of insulin secretion and insulin action will be necessary to design effective countermeasures against muscle loss, and we advance the "disposition index" as an essential model to be used in the clinical management of space flight-induced muscle loss.

  9. Cytosolic and Calcium-Independent Phospholipases A2 Activation and Prostaglandins E2 Are Associated with Escherichia coli-Induced Reduction of Insulin Secretion in INS-1E Cells.

    PubMed

    Caporarello, Nunzia; Salmeri, Mario; Scalia, Marina; Motta, Carla; Parrino, Cristina; Frittitta, Lucia; Olivieri, Melania; Cristaldi, Martina; Avola, Roberto; Bramanti, Vincenzo; Toscano, Maria Antonietta; Anfuso, Carmelina Daniela; Lupo, Gabriella

    2016-01-01

    It is suspected that microbial infections take part in the pathogenesis of diabetes mellitus type 1 (T1DM). Glucose-induced insulin secretion is accompanied by the release of free arachidonic acid (AA) mainly by cytosolic- and calcium independent phospholipases A2 (cPLA2 and iPLA2). Insulinoma cell line (INS-1E) was infected with E. coli isolated from the blood culture of a patient with sepsis. Invasion assay, Scanning Electron Microscopy and Transmission Electron Microscopy demonstrated the capacity of E. coli to enter cells, which was reduced by PLA2 inhibitors. Glucose-induced insulin secretion was significantly increased after acute infection (8h) but significantly decreased after chronic infection (72h). PLA2 activities, cPLA2, iPLA2, phospho-cPLA2, and COX-2 expressions were increased after acute and, even more, after chronic E. coli infection. The silencing of the two isoforms of PLA2s, with specific cPLA2- or iPLA2-siRNAs, reduced insulin secretion after acute infection and determined a rise in insulin release after chronic infection. Prostaglandins E2 (PGE2) production was significantly elevated in INS-1E after long-term E. coli infection and the restored insulin secretion in presence of L798106, a specific EP3 antagonist, and NS-398, a COX-2 inhibitor, and the reduction of insulin secretion in presence of sulprostone, a specific EP3 agonist, revealed their involvement in the effects triggered by bacterial infection. The results obtained demonstrated that cPLA2 and iPLA2 play a key role in insulin secretion process after E. coli infection. The high concentration of AA released is transformed into PGE2, which could be responsible for the reduced insulin secretion.

  10. Cytosolic and Calcium-Independent Phospholipases A2 Activation and Prostaglandins E2 Are Associated with Escherichia coli-Induced Reduction of Insulin Secretion in INS-1E Cells

    PubMed Central

    Scalia, Marina; Motta, Carla; Parrino, Cristina; Frittitta, Lucia; Olivieri, Melania; Cristaldi, Martina; Avola, Roberto; Bramanti, Vincenzo; Toscano, Maria Antonietta; Anfuso, Carmelina Daniela; Lupo, Gabriella

    2016-01-01

    It is suspected that microbial infections take part in the pathogenesis of diabetes mellitus type 1 (T1DM). Glucose-induced insulin secretion is accompanied by the release of free arachidonic acid (AA) mainly by cytosolic- and calcium independent phospholipases A2 (cPLA2 and iPLA2). Insulinoma cell line (INS-1E) was infected with E. coli isolated from the blood culture of a patient with sepsis. Invasion assay, Scanning Electron Microscopy and Transmission Electron Microscopy demonstrated the capacity of E. coli to enter cells, which was reduced by PLA2 inhibitors. Glucose-induced insulin secretion was significantly increased after acute infection (8h) but significantly decreased after chronic infection (72h). PLA2 activities, cPLA2, iPLA2, phospho-cPLA2, and COX-2 expressions were increased after acute and, even more, after chronic E. coli infection. The silencing of the two isoforms of PLA2s, with specific cPLA2- or iPLA2-siRNAs, reduced insulin secretion after acute infection and determined a rise in insulin release after chronic infection. Prostaglandins E2 (PGE2) production was significantly elevated in INS-1E after long-term E. coli infection and the restored insulin secretion in presence of L798106, a specific EP3 antagonist, and NS-398, a COX-2 inhibitor, and the reduction of insulin secretion in presence of sulprostone, a specific EP3 agonist, revealed their involvement in the effects triggered by bacterial infection. The results obtained demonstrated that cPLA2 and iPLA2 play a key role in insulin secretion process after E. coli infection. The high concentration of AA released is transformed into PGE2, which could be responsible for the reduced insulin secretion. PMID:27631977

  11. Fenofibrate Decreases Insulin Clearance and Insulin Secretion to Maintain Insulin Sensitivity.

    PubMed

    Ramakrishnan, Sadeesh K; Russo, Lucia; Ghanem, Simona S; Patel, Payal R; Oyarce, Ana Maria; Heinrich, Garrett; Najjar, Sonia M

    2016-11-11

    High fat diet reduces the expression of CEACAM1 (carcinoembryonic antigen-related cell adhesion molecule 1), a transmembrane glycoprotein that promotes insulin clearance and down-regulates fatty acid synthase activity in the liver upon its phosphorylation by the insulin receptor. Because peroxisome proliferator-activated receptor α (PPARα) transcriptionally suppresses CEACAM1 expression, we herein examined whether high fat down-regulates CEACAM1 expression in a PPARα-dependent mechanism. By activating PPARα, the lipid-lowering drug fenofibrate reverses dyslipidemia and improves insulin sensitivity in type 2 diabetes in part by promoting fatty acid oxidation. Despite reducing glucose-stimulated insulin secretion, fenofibrate treatment does not result in insulin insufficiency. To examine whether this is mediated by a parallel decrease in CEACAM1-dependent hepatic insulin clearance pathways, we fed wild-type and Pparα(-/-) null mice a high fat diet supplemented with either fenofibrate or Wy14643, a selective PPARα agonist, and examined their effect on insulin metabolism and action. We demonstrated that the decrease in insulin secretion by fenofibrate and Wy14643 is accompanied by reduction in insulin clearance in wild-type but not Pparα(-/-) mice, thereby maintaining normoinsulinemia and insulin sensitivity despite continuous high fat intake. Intact insulin secretion in L-CC1 mice with protected hepatic insulin clearance and CEACAM1 levels provides in vivo evidence that insulin secretion responds to changes in insulin clearance to maintain physiologic insulin and glucose homeostasis. These results also emphasize the relevant role of hepatic insulin extraction in regulating insulin sensitivity. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

  12. Glucagon-like peptide 1 stimulates insulin secretion via inhibiting RhoA/ROCK signaling and disassembling glucotoxicity-induced stress fibers.

    PubMed

    Kong, Xiangchen; Yan, Dan; Sun, Jiangming; Wu, Xuerui; Mulder, Hindrik; Hua, Xianxin; Ma, Xiaosong

    2014-12-01

    Chronic hyperglycemia leads to pancreatic β-cell dysfunction characterized by diminished glucose-stimulated insulin secretion (GSIS), but the precise cellular processes involved are largely unknown. Here we show that pancreatic β-cells chronically exposed to a high glucose level displayed substantially increased amounts of stress fibers compared with β-cells cultured at a low glucose level. β-Cells at high glucose were refractory to glucose-induced actin cytoskeleton remodeling and insulin secretion. Importantly, F-actin depolymerization by either cytochalasin B or latrunculin B restored glucotoxicity-diminished GSIS. The effects of glucotoxicity on increasing stress fibers and reducing GSIS were reversed by Y-27632, a Rho-associated kinase (ROCK)-specific inhibitor, which caused actin depolymerization and enhanced GSIS. Notably, glucagon-like peptide-1-(7-36) amide (GLP-1), a peptide hormone that stimulates GSIS at both normal and hyperglycemic conditions, also reversed glucotoxicity-induced increase of stress fibers and reduction of GSIS. In addition, GLP-1 inhibited glucotoxicity-induced activation of RhoA/ROCK and thereby resulted in actin depolymerization and potentiation of GSIS. Furthermore, this effect of GLP-1 was mimicked by cAMP-increasing agents forskolin and 3-isobutyl-1-methylxanthine as well as the protein kinase A agonist 6-Bnz-cAMP-AM whereas it was abolished by the protein kinase A inhibitor Rp-Adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt. To establish a clinical relevance of our findings, we examined the association of genetic variants of RhoA/ROCK with metabolic traits in homeostasis model assessment index of insulin resistance. Several single-nucleotide polymorphisms in and around RHOA were associated with elevated fasting insulin and homeostasis model assessment index of insulin resistance, suggesting a possible role in metabolic dysregulation. Collectively these findings unravel a novel mechanism whereby GLP-1

  13. Sasa borealis leaves extract improves insulin resistance by modulating inflammatory cytokine secretion in high fat diet-induced obese C57/BL6J mice

    PubMed Central

    Yang, Jung-Hwa; Lim, Hyeon-Sook

    2010-01-01

    Obesity is considered a mild inflammatory state, and the secretion of inflammation-related cytokines rises as adipose tissue expands. Inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interlukin 6 (IL-6) and monocyte-chemoattractant protein 1 (MCP-1), are modulated by adipose tissue and known to play an important role in insulin resistance which is the common characteristics of obesity related disorders. In this study we analyzed the effects of Sasa borealis leaves extract on inflammatory cytokines and insulin resistance in diet induced obese C57/BL6J mice. The obese state was induced by a high fat diet for 20 weeks and then the mice were divided into two groups; obese control group (OBC, n = 7) and experimental group (OB-SBE, n = 7). The OBC group was fed a high fat diet and the OB-SBE group was fed a high fat diet containing 5% Sasa borealis leaves extract (SBE) for 12 weeks. We also used mice fed a standard diet as a normal control (NC, n = 7). The body weight and adipose tissue weight in the OB group were significantly higher than those in the NC group. The effects of the high fat diet were reduced by SBE treatments, and the body weight and adipose tissue deposition in the OB-SBE group were significantly decreased compared to the OBC group. The OBC group showed higher serum glucose and insulin levels which resulted in a significant increase of incremental area under the curve (IAUC) and HOMA-IR than the NC group. Also, serum leptin, TNF-α, and IL-6 levels were significantly higher in the OBC group than in the NC group. In contrast, the OB-SBE group showed a reversal in the metabolic defects, including a decrease in glucose, insulin, IAUC, HOMA-IR, TNF-α, IL-6 and leptin levels. These results suggest that BSE can suppress increased weight gain and/or fat deposition induced by a high fat diet and theses effects are accompanied by modulation of the inflammatory cytokines, TNF-α and IL-6 secretion resulting in improved insulin resistance. PMID

  14. Bilobalide abates inflammation, insulin resistance and secretion of angiogenic factors induced by hypoxia in 3T3-L1 adipocytes by controlling NF-κB and JNK activation.

    PubMed

    Priyanka, A; Sindhu, G; Shyni, G L; Preetha Rani, M R; Nisha, V M; Raghu, K G

    2017-01-01

    Obesity leads to inflammation and insulin resistance in adipose tissue. Hypoxia, observed in obese adipose tissue is suggested as a major cause of inflammation and insulin resistance in obesity. However, the role of hypoxia in adipose tissue during obesity and insulin resistance was not well established. Here we mainly explored the crosstalk between hypoxia induced inflammation, and insulin resistance and also secretion of angiogenic factors in 3T3-L1 adipocytes and possible reversal with bilobalide. Hypoxia for 24h significantly (P≤0.05) increased the secretion of MCP-1 (4.59 fold), leptin (2.96 fold) and reduced adiponectin secretion (2.93 fold). In addition, the mRNA level of resistin (6.8 fold) and TLR4 receptors (8.8 fold) was upregulated in hypoxic adipocytes. The release of inflammatory cytokines and expression of TLR4 receptors led to activation of JNK and NF-κB signalling. We further investigated the effects of JNK and NF-κB activation on insulin signalling receptors. The present study showed increased (P≤0.05) serine 307 phosphorylation of IRS-1 (1.9 fold) and decreased expression of IRS-2 (0.53 fold) in hypoxic group showing hypoxia induced impairment in insulin signalling. Hypoxia significantly (P≤0.05) increased basal glucose uptake (3.3 fold) as well as GLUT-1 expression in adipocytes indicating GLUT-1 mediated glucose uptake. Hypoxia for 24h significantly increased (P≤0.05) the expression of angiogenic factors. Bilobalide protected adipocytes from hypoxia induced inflammation and insulin resistance mainly by reducing inflammatory adipokine secretion, improving adiponectin secretion, reducing NF-κB/JNK activation, and inhibiting serine phosphorylation of IRS-1 receptors of insulin signalling pathway. Copyright © 2016 Elsevier B.V. All rights reserved.

  15. Transcriptional regulation of the miR-212/miR-132 cluster in insulin-secreting β-cells by cAMP-regulated transcriptional co-activator 1 and salt-inducible kinases.

    PubMed

    Malm, Helena Anna; Mollet, Inês G; Berggreen, Christine; Orho-Melander, Marju; Esguerra, Jonathan Lou S; Göransson, Olga; Eliasson, Lena

    2016-03-15

    MicroRNAs are central players in the control of insulin secretion, but their transcriptional regulation is poorly understood. Our aim was to investigate cAMP-mediated transcriptional regulation of the miR-212/miR-132 cluster and involvement of further upstream proteins in insulin secreting β-cells. cAMP induced by forskolin+IBMX or GLP-1 caused increased expression of miR-212/miR-132, and elevated phosphorylation of cAMP-response-element-binding-protein (CREB)/Activating-transcription-factor-1 (ATF1) and Salt-Inducible-Kinases (SIKs). CyclicAMP-Regulated Transcriptional Co-activator-1 (CRTC1) was concomitantly dephosphorylated and translocated to the nucleus. Silencing of miR-212/miR-132 reduced, and overexpression of miR-212 increased, glucose-stimulated insulin secretion. Silencing of CRTC1 expression resulted in decreased insulin secretion and miR-212/miR-132 expression, while silencing or inhibition of SIKs was associated with increased expression of the microRNAs and dephosphorylation of CRTC1. CRTC1 protein levels were reduced after silencing of miR-132, suggesting feed-back regulation. Our data propose cAMP-dependent co-regulation of miR-212/miR-132, in part mediated through SIK-regulated CRTC1, as an important factor for fine-tuned regulation of insulin secretion.

  16. LIM-homeodomain transcription factor Isl-1 mediates kisspeptin's effect on insulin secretion in mice.

    PubMed

    Chen, Juan; Fu, Rui; Cui, Yan; Pan, Jirong; Li, Yushan; Zhang, Xiaoxin; Evans, Sylvia M; Cui, Sheng; Liu, Jiali

    2014-08-01

    Kisspeptin and the G protein-coupled receptor 54 (GPR54) are highly abundant in the pancreas. In addition, circulating kisspeptin directly influences insulin secretion through GPR54. However, the mechanisms by which kisspeptin affects insulin release are unclear. The LIM-homeodomain transcription factor, Isl-1, is expressed in all pancreatic islet cells and is involved in regulating both islet development and insulin secretion. We therefore investigated potential interactions between kisspeptin and Isl-1. Our results demonstrate that Isl-1 and GPR54 are coexpressed in mouse pancreatic islet β-cells and NIT cells. Both in vitro and in vivo results demonstrate that kisspeptin-54 (KISS-54) inhibits Isl-1 expression and insulin secretion and both the in vivo and in vitro effects of KISS-54 on insulin gene expression and secretion are abolished when an Isl-1-inducible knockout model is used. Moreover, our results demonstrate that the direct action of KISS-54 on insulin secretion is mediated by Isl-1. Our results further show that KISS-54 influences Isl-1 expression and insulin secretion through the protein kinase C-ERK1/2 pathway. Conversely, insulin has a feedback loop via the Janus kinase-phosphatidylinositol 3-kinase pathway regulating kisspeptin expression and secretion. These findings are important in understanding mechanisms of insulin secretion and metabolism in diabetes.

  17. Asparagus officinalis extract controls blood glucose by improving insulin secretion and β-cell function in streptozotocin-induced type 2 diabetic rats.

    PubMed

    Hafizur, Rahman Md; Kabir, Nurul; Chishti, Sidra

    2012-11-14

    The aim of the present study was to evaluate the anti-diabetic mechanism of Asparagus officinalis, a dietary agent used for the management of diabetes. Streptozotocin (90 mg/kg) was injected in 2-d-old Wistar rat pups to induce non-obese type 2 diabetes. After confirmation of diabetes on the 13th week, diabetic rats were treated with a methanolic extract of A. officinalis seeds (250 and 500 mg/kg per d) or glibenclamide for 28 d. After the treatment, fasting blood glucose, serum insulin and total antioxidant status were measured. The pancreas was examined by haematoxylin-eosin staining and immunostained β- and α-cells were observed using a fluorescence microscope. Treatment of the diabetic rats with the A. officinalis extract at doses of 250 and 500 mg/kg suppressed the elevated blood glucose in a dose- and time-dependent manner. The 500 mg/kg, but not 250 mg/kg, dose significantly improved serum insulin levels in the diabetic rats. The insulin:glucose ratio was significantly increased at both doses in the A. officinalis-treated rats. Both qualitative and quantitative improvements in β-cell function were found in the islets of the A. officinalis-treated rats. The extract showed potent antioxidant activity in an in vitro assay and also improved the total antioxidant status in vivo. In most cases, the efficacy of A. officinalis (500 mg/kg) was very similar to a standard anti-diabetic drug, glibenclamide. Thus, the present study suggests that A. officinalis extract exerts anti-diabetic effects by improving insulin secretion and β-cell function, as well as the antioxidant status.

  18. Simvastatin Impairs Insulin Secretion by Multiple Mechanisms in MIN6 Cells.

    PubMed

    Yaluri, Nagendra; Modi, Shalem; López Rodríguez, Maykel; Stančáková, Alena; Kuusisto, Johanna; Kokkola, Tarja; Laakso, Markku

    2015-01-01

    Statins are widely used in the treatment of hypercholesterolemia and are efficient in the prevention of cardiovascular disease. Molecular mechanisms explaining statin-induced impairment in insulin secretion remain largely unknown. In the current study, we show that simvastatin decreased glucose-stimulated insulin secretion in mouse pancreatic MIN6 β-cells by 59% and 79% (p<0.01) at glucose concentration of 5.5 mmol/l and 16.7 mmol/l, respectively, compared to control, whereas pravastatin did not impair insulin secretion. Simvastatin induced decrease in insulin secretion occurred through multiple targets. In addition to its established effects on ATP-sensitive potassium channels (p = 0.004) and voltage-gated calcium channels (p = 0.004), simvastatin suppressed insulin secretion stimulated by muscarinic M3 or GPR40 receptor agonists (Tak875 by 33%, p = 0.002; GW9508 by 77%, p = 0.01) at glucose level of 5.5 mmol/l, and inhibited calcium release from the endoplasmic reticulum. Impaired insulin secretion caused by simvastatin treatment were efficiently restored by GPR119 or GLP-1 receptor stimulation and by direct activation of cAMP-dependent signaling pathways with forskolin. The effects of simvastatin treatment on insulin secretion were not affected by the presence of hyperglycemia. Our observation of the opposite effects of simvastatin and pravastatin on glucose-stimulated insulin secretion is in agreement with previous reports showing that simvastatin, but not pravastatin, was associated with increased risk of incident diabetes.

  19. Deletion of GPR40 Impairs Glucose-Induced Insulin Secretion In Vivo in Mice Without Affecting Intracellular Fuel Metabolism in Islets

    PubMed Central

    Alquier, Thierry; Peyot, Marie-Line; Latour, Martin G.; Kebede, Melkam; Sorensen, Christina M.; Gesta, Stephane; Ronald Kahn, C.; Smith, Richard D.; Jetton, Thomas L.; Metz, Thomas O.; Prentki, Marc; Poitout, Vincent

    2009-01-01

    OBJECTIVE The G-protein–coupled receptor GPR40 mediates fatty acid potentiation of glucose-stimulated insulin secretion, but its contribution to insulin secretion in vivo and mechanisms of action remain uncertain. This study was aimed to ascertain whether GPR40 controls insulin secretion in vivo and modulates intracellular fuel metabolism in islets. RESEARCH DESIGN AND METHODS Insulin secretion and sensitivity were assessed in GPR40 knockout mice and their wild-type littermates by hyperglycemic clamps and hyperinsulinemic euglycemic clamps, respectively. Transcriptomic analysis, metabolic studies, and lipid profiling were used to ascertain whether GPR40 modulates intracellular fuel metabolism in islets. RESULTS Both glucose- and arginine-stimulated insulin secretion in vivo were decreased by ∼60% in GPR40 knockout fasted and fed mice, without changes in insulin sensitivity. Neither gene expression profiles nor intracellular metabolism of glucose and palmitate in isolated islets were affected by GPR40 deletion. Lipid profiling of isolated islets revealed that the increase in triglyceride and decrease in lyso-phosphatidylethanolamine species in response to palmitate in vitro was similar in wild-type and knockout islets. In contrast, the increase in intracellular inositol phosphate levels observed in wild-type islets in response to fatty acids in vitro was absent in knockout islets. CONCLUSIONS These results indicate that deletion of GPR40 impairs insulin secretion in vivo not only in response to fatty acids but also to glucose and arginine, without altering intracellular fuel metabolism in islets, via a mechanism that may involve the generation of inositol phosphates downstream of GPR40 activation. PMID:19720802

  20. A Unifying Organ Model of Pancreatic Insulin Secretion

    PubMed Central

    De Gaetano, Andrea; Gaz, Claudio; Palumbo, Pasquale; Panunzi, Simona

    2015-01-01

    The secretion of insulin by the pancreas has been the object of much attention over the past several decades. Insulin is known to be secreted by pancreatic β-cells in response to hyperglycemia: its blood concentrations however exhibit both high-frequency (period approx. 10 minutes) and low-frequency oscillations (period approx. 1.5 hours). Furthermore, characteristic insulin secretory response to challenge maneuvers have been described, such as frequency entrainment upon sinusoidal glycemic stimulation; substantial insulin peaks following minimal glucose administration; progressively strengthened insulin secretion response after repeated administration of the same amount of glucose; insulin and glucose characteristic curves after Intra-Venous administration of glucose boli in healthy and pre-diabetic subjects as well as in Type 2 Diabetes Mellitus. Previous modeling of β-cell physiology has been mainly directed to the intracellular chain of events giving rise to single-cell or cell-cluster hormone release oscillations, but the large size, long period and complex morphology of the diverse responses to whole-body glucose stimuli has not yet been coherently explained. Starting with the seminal work of Grodsky it was hypothesized that the population of pancreatic β-cells, possibly functionally aggregated in islets of Langerhans, could be viewed as a set of independent, similar, but not identical controllers (firing units) with distributed functional parameters. The present work shows how a single model based on a population of independent islet controllers can reproduce very closely a diverse array of actually observed experimental results, with the same set of working parameters. The model’s success in reproducing a diverse array of experiments implies that, in order to understand the macroscopic behaviour of the endocrine pancreas in regulating glycemia, there is no need to hypothesize intrapancreatic pacemakers, influences between different islets of Langerhans

  1. Optical Control of Insulin Secretion Using an Incretin Switch.

    PubMed

    Broichhagen, Johannes; Podewin, Tom; Meyer-Berg, Helena; von Ohlen, Yorrick; Johnston, Natalie R; Jones, Ben J; Bloom, Stephen R; Rutter, Guy A; Hoffmann-Röder, Anja; Hodson, David J; Trauner, Dirk

    2015-12-14

    Incretin mimetics are set to become a mainstay of type 2 diabetes treatment. By acting on the pancreas and brain, they potentiate insulin secretion and induce weight loss to preserve normoglycemia. Despite this, incretin therapy has been associated with off-target effects, including nausea and gastrointestinal disturbance. A novel photoswitchable incretin mimetic based upon the specific glucagon-like peptide-1 receptor (GLP-1R) agonist liraglutide was designed, synthesized, and tested. This peptidic compound, termed LirAzo, possesses an azobenzene photoresponsive element, affording isomer-biased GLP-1R signaling as a result of differential activation of second messenger pathways in response to light. While the trans isomer primarily engages calcium influx, the cis isomer favors cAMP generation. LirAzo thus allows optical control of insulin secretion and cell survival.

  2. The acquisition of an insulin-secreting phenotype by HGF-treated rat pancreatic ductal cells (ARIP) is associated with the development of susceptibility to cytokine-induced apoptosis.

    PubMed

    Anastasi, E; Santangelo, C; Bulotta, A; Dotta, F; Argenti, B; Mincione, C; Gulino, A; Maroder, M; Perfetti, R; Di Mario, U

    2005-04-01

    The elucidation of mechanisms regulating the regeneration and survival of pancreatic beta cells has fundamental implications in the cell therapy of type 1 diabetes. The present study had the following three aims: 1. to investigate whether pancreatic ductal epithelial cells can be induced to differentiate into insulin-producing cells by exposing them to hepatocyte growth factor (HGF); 2. to characterize some of the molecular events leading to their differentiation toward a beta-cell-like phenotype; 3. to evaluate the susceptibility of newly differentiated insulin-secreting cells to cytokine-induced apoptosis, a mechanism of beta-cell destruction occurring in type 1 diabetes. We demonstrated that HGF-treated rat pancreatic ductal cell line (ARIP) cells acquired the capability to transcribe the insulin gene and translate its counterpart protein. HGF-treated cells also exhibited a glucose-dependent capability to secrete insulin into the cultured medium. Expression analysis of some of the genes regulating pancreatic beta-cell differentiation revealed a time-dependent transcription of neurogenin-3 and Neuro-D in response to HGF. Finally, we determined the susceptibility to proinflammatory cytokine (PTh1)-induced apoptosis by incubating HGF-treated and untreated ARIP cells with a cocktail of interleukin-1 beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). Such treatment induced apoptotic death, as determined by the TUNEL technique, in about 40% of HGF-treated, insulin-secreting ARIP cells, while untreated ARIP cells were resistant to PTh1-induced apoptosis. In conclusion, we showed that HGF promotes the differentiation of ARIP cells into pancreatic beta-cell-like cells, and that the differentiation toward an insulin-secreting phenotype is associated with the appearance of susceptibility to cytokine-induced apoptosis.

  3. Insulin secretion and action in North Indian women during pregnancy.

    PubMed

    Arora, G P; Almgren, P; Thaman, R G; Pal, A; Groop, L; Vaag, A; Prasad, R B; Brøns, C

    2017-10-01

    The relative roles(s) of impaired insulin secretion vs. insulin resistance in the development of gestational diabetes mellitus depend upon multiple risk factors and diagnostic criteria. Here, we explored their relative contribution to gestational diabetes as defined by the WHO 1999 (GDM1999) and adapted WHO 2013 (GDM2013) criteria, excluding the 1-h glucose value, in a high-risk Indian population from Punjab. Insulin secretion (HOMA2-B) and insulin action (HOMA2-IR) were assessed in 4665 Indian women with or without gestational diabetes defined by the GDM1999 or adapted GDM2013 criteria. Gestational diabetes defined using both criteria was associated with decreased insulin secretion compared with pregnant women with normal glucose tolerance. Women with gestational diabetes defined by the adapted GDM2013, but not GDM1999 criteria, were more insulin resistant than pregnant women with normal glucose tolerance, and furthermore displayed lower insulin secretion than GDM1999 women. Urban habitat, illiteracy, high age and low BMI were independently associated with reduced insulin secretion, whereas Sikh religion, increasing age and BMI, as well as a family history of diabetes were independently associated with increased insulin resistance. Gestational diabetes risk factors influence insulin secretion and action in North Indian women in a differential manner. Gestational diabetes classified using the adapted GDM2013 compared with GDM1999 criteria is associated with more severe impairments of insulin secretion and action. © 2017 Diabetes UK.

  4. The effect of fasting, diet, and actinomycin D on insulin secretion in the rat

    PubMed Central

    Grey, N. J.; Goldring, S.; Kipnis, D. M.

    1970-01-01

    The present studies were performed to elucidate the mechanisms responsible for the impairment of glucose-stimulated insulin secretion observed in fasting. Rats fasted for 48 hr displayed marked impairment in their insulin secretory response to both oral and intravenous glucose. Glucose-stimulated insulin secretion was restored within 24 hr by refeeding; actinomycin D given before refeeding blocked the expected return of normal glucose-stimulated insulin secretion despite adequate food intake. Fasted rats refed a diet devoid of carbohydrate failed to display a return of normal insulin secretory responsiveness to oral glucose in contrast to rats fed isocalorically a high carbohydrate diet. Differences in insulin secretion in fed, fasted, and fasted-refed rats could not be attributed to changes in pancreatic insulin content. There was no significant difference in the insulin secretory response to aminophylline of fed, fasted, or fasted-refed rats. The intermittent pulsing of fasted rats with hyperglycemic episodes by the injection of small amounts of glucose (500 mg) intraperitoneally every 8 hr ameliorated the impairment of glucose-stimulated insulin secretion characteristic of the fasting state. These results suggest that the impairment of glucose-stimulated insulin secretion during fasting and its restoration by refeeding are regulated by changes in a glucose-inducible enzyme system in the pancreatic beta cell. PMID:5441542

  5. Impaired insulin secretion and glucose intolerance in synaptotagmin-7 null mutant mice

    PubMed Central

    Gustavsson, Natalia; Lao, Ye; Maximov, Anton; Chuang, Jen-Chieh; Kostromina, Elena; Repa, Joyce J.; Li, Cai; Radda, George K.; Südhof, Thomas C.; Han, Weiping

    2008-01-01

    Vertebrates express at least 15 different synaptotagmins with the same domain structure but diverse localizations and tissue distributions. Synaptotagmin-1,-2, and -9 act as calcium sensors for the fast phrase of neurotransmitter release, and synaptotagmin-12 acts as a calcium-independent modulator of release. The exact functions of the remaining 11 synaptotagmins, however, have not been established. By analogy to the role of synaptotagmin-1, -2, and -9 in neurotransmission, these other synaptotagmins may serve as Ca2+ transducers regulating other Ca2+-dependent membrane processes, such as insulin secretion in pancreatic β-cells. Of these other synaptotagmins, synaptotagmin-7 is one of the most abundant and is present in pancreatic β-cells. To determine whether synaptotagmin-7 regulates Ca2+-dependent insulin secretion, we analyzed synaptotagmin-7 null mutant mice for glucose tolerance and insulin release. Here, we show that synaptotagmin-7 is required for the maintenance of systemic glucose tolerance and glucose-stimulated insulin secretion. Mutant mice have normal insulin sensitivity, insulin production, islet architecture and ultrastructural organization, and metabolic and calcium responses but exhibit impaired glucose-induced insulin secretion, indicating a calcium-sensing defect during insulin-containing secretory granule exocytosis. Taken together, our findings show that synaptotagmin-7 functions as a positive regulator of insulin secretion and may serve as a calcium sensor controlling insulin secretion in pancreatic β cells. PMID:18308938

  6. Impaired insulin secretion and glucose intolerance in synaptotagmin-7 null mutant mice.

    PubMed

    Gustavsson, Natalia; Lao, Ye; Maximov, Anton; Chuang, Jen-Chieh; Kostromina, Elena; Repa, Joyce J; Li, Cai; Radda, George K; Südhof, Thomas C; Han, Weiping

    2008-03-11

    Vertebrates express at least 15 different synaptotagmins with the same domain structure but diverse localizations and tissue distributions. Synaptotagmin-1,-2, and -9 act as calcium sensors for the fast phrase of neurotransmitter release, and synaptotagmin-12 acts as a calcium-independent modulator of release. The exact functions of the remaining 11 synaptotagmins, however, have not been established. By analogy to the role of synaptotagmin-1, -2, and -9 in neurotransmission, these other synaptotagmins may serve as Ca(2+) transducers regulating other Ca(2+)-dependent membrane processes, such as insulin secretion in pancreatic beta-cells. Of these other synaptotagmins, synaptotagmin-7 is one of the most abundant and is present in pancreatic beta-cells. To determine whether synaptotagmin-7 regulates Ca(2+)-dependent insulin secretion, we analyzed synaptotagmin-7 null mutant mice for glucose tolerance and insulin release. Here, we show that synaptotagmin-7 is required for the maintenance of systemic glucose tolerance and glucose-stimulated insulin secretion. Mutant mice have normal insulin sensitivity, insulin production, islet architecture and ultrastructural organization, and metabolic and calcium responses but exhibit impaired glucose-induced insulin secretion, indicating a calcium-sensing defect during insulin-containing secretory granule exocytosis. Taken together, our findings show that synaptotagmin-7 functions as a positive regulator of insulin secretion and may serve as a calcium sensor controlling insulin secretion in pancreatic beta cells.

  7. D-chiro-inositol glycan stimulates insulin secretion in pancreatic β cells.

    PubMed

    Lazarenko, Roman; Geisler, Jessica; Bayliss, Douglas; Larner, Joseph; Li, Chien

    2014-04-25

    Insulin has been shown to act on pancreatic β cells to regulate its own secretion. Currently the mechanism underlying this effect is unclear. INS-2, a novel inositol glycan pseudo-disaccharide containing D-chiro-inositol and galactosamine, has been shown to function as an insulin mimetic and a putative insulin mediator. In the present study we found that INS-2 stimulates insulin secretion in MIN6 β cells and potentiates glucose stimulated insulin secretion in isolated mouse islets. Importantly, INS-2 failed to potentiate insulin secretion induced by tolbutamide, which stimulates insulin release by closing ATP sensitive potassium channels (KATP). Electrophysiological studies showed that INS-2 inhibited sulfonylurea-sensitive KATP conductance. The effect of INS-2 on inhibiting KATP channel is mediated by protein phosphatase 2C (PP2C), as knocking down PP2C expression in MIN6 cells by PP2C small hairpin RNA completely abolished the effect of INS-2 on KATP and consequently attenuated INS-2 induced insulin secretion. In conclusion, the present study identifies a novel mechanism involving PP2C in regulating KATP channel activity and consequently insulin secretion.

  8. Aβ-Induced Insulin Resistance and the Effects of Insulin on the Cholesterol Synthesis Pathway and Aβ Secretion in Neural Cells.

    PubMed

    Najem, Dema; Bamji-Mirza, Michelle; Yang, Ze; Zhang, Wandong

    2016-06-01

    Alzheimer's disease (AD) is characterized by amyloid-β (Aβ) toxicity, tau pathology, insulin resistance, neuroinflammation, and dysregulation of cholesterol homeostasis, all of which play roles in neurodegeneration. Insulin has polytrophic effects on neurons and may be at the center of these pathophysiological changes. In this study, we investigated possible relationships among insulin signaling and cholesterol biosynthesis, along with the effects of Aβ42 on these pathways in vitro. We found that neuroblastoma 2a (N2a) cells transfected with the human gene encoding amyloid-β protein precursor (AβPP) (N2a-AβPP) produced Aβ and exhibited insulin resistance by reduced p-Akt and a suppressed cholesterol-synthesis pathway following insulin treatment, and by increased phosphorylation of insulin receptor subunit-1 at serine 612 (p-IRS-S612) as compared to parental N2a cells. Treatment of human neuroblastoma SH-SY5Y cells with Aβ42 also increased p-IRS-S612, suggesting that Aβ42 is responsible for insulin resistance. The insulin resistance was alleviated when N2a-AβPP cells were treated with higher insulin concentrations. Insulin increased Aβ release from N2a-AβPP cells, by which it may promote Aβ clearance. Insulin increased cholesterol-synthesis gene expression in SH-SY5Y and N2a cells, including 24-dehydrocholesterol reductase (DHCR24) and 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCR) through sterol-regulatory element-binding protein-2 (SREBP2). While Aβ42-treated SH-SY5Y cells exhibited increased HMGCR expression and c-Jun phosphorylation as pro-inflammatory responses, they also showed down-regulation of neuro-protective/anti-inflammatory DHCR24. These results suggest that Aβ42 may cause insulin resistance, activate JNK for c-Jun phosphorylation, and lead to dysregulation of cholesterol homeostasis, and that enhancing insulin signaling may relieve the insulin-resistant phenotype and the dysregulated cholesterol-synthesis pathway to promote A

  9. Vitamin D, Insulin Secretion, Sensitivity, and Lipids

    PubMed Central

    Grimnes, Guri; Figenschau, Yngve; Almås, Bjørg; Jorde, Rolf

    2011-01-01

    OBJECTIVE Vitamin D deficiency is associated with an unfavorable metabolic profile in observational studies. The intention was to compare insulin sensitivity (the primary end point) and secretion and lipids in subjects with low and high serum 25(OH)D (25-hydroxyvitamin D) levels and to assess the effect of vitamin D supplementation on the same outcomes among the participants with low serum 25(OH)D levels. RESEARCH DESIGN AND METHODS Participants were recruited from a population-based study (the Tromsø Study) based on their serum 25(OH)D measurements. A 3-h hyperglycemic clamp was performed, and the participants with low serum 25(OH)D levels were thereafter randomized to receive capsules of 20,000 IU vitamin D3 or identical-looking placebo twice weekly for 6 months. A final hyperglycemic clamp was then performed. RESULTS The 52 participants with high serum 25(OH)D levels (85.6 ± 13.5 nmol/L [mean ± SD]) had significantly higher insulin sensitivity index (ISI) and lower HbA1c and triglycerides (TGs) than the 108 participants with low serum 25(OH)D (40.3 ± 12.8 nmol/L), but the differences in ISI and TGs were not significant after adjustments. After supplementation, serum 25(OH)D was 142.7 ± 25.7 and 42.9 ± 17.3 nmol/L in 49 of 51 completing participants randomized to vitamin D and 45 of 53 randomized to placebo, respectively. At the end of the study, there were no statistically significant differences in the outcome variables between the two groups. CONCLUSIONS Vitamin D supplementation to apparently healthy subjects with insufficient serum 25(OH)D levels does not improve insulin sensitivity or secretion or serum lipid profile. PMID:21911741

  10. The possible mechanisms by which maternal hypothyroidism impairs insulin secretion in adult male offspring in rats.

    PubMed

    Karbalaei, Narges; Ghasemi, Asghar; Hedayati, Mehdi; Godini, Aliashraf; Zahediasl, Saleh

    2014-04-01

    Previous studies have recently shown that maternal hypothyroidism leads to impaired glucose metabolism and reduced insulin secretion in adult offspring in rats. The aim of this study was to locate the defect in the insulin secretion pathway induced by maternal hypothyroidism. Pregnant Wistar rats were divided into two groups; the control group consumed water, while the hypothyroid (FH) group received water containing 0.025% 6-propyl-2-thiouracil during gestation. An intravenous glucose tolerance test was carried out on 5-month-old male offspring. In in vitro studies, the effects of various secretagogues and inhibitors acting at different levels of the insulin secretion cascade were investigated, and insulin content, insulin secretion and glucokinase activity of the islets were compared. Although insulin content of the FH islets did not differ from that of control islets, insulin secretion from FH islets was reduced when it was challenged by glucose or arginine. Compared with control islets, activities of both hexokinase and glucokinase were also significantly decreased in the FH islets. Although, in both groups, increasing glibenclamide and nifedipine concentrations in the presence of 16.7 mmol l(-1) glucose increased and decreased insulin secretion, respectively, the percentage of changes in secretion of FH islets was significantly lower compared with control islets. The response of FH islets to high extracellular potassium concentration and diazoxide was also significantly lower than that of the control islets. These findings demonstrate that impaired insulin secretion in the FH group is probably related to alterations in different steps of the insulin secretion pathway and not in the insulin pool of β-cells.

  11. Regulation of insulin secretion and proinsulin biosynthesis by succinate.

    PubMed

    Attali, Veronique; Parnes, Marcela; Ariav, Yafa; Cerasi, Erol; Kaiser, Nurit; Leibowitz, Gil

    2006-11-01

    Succinate stimulates insulin secretion and proinsulin biosynthesis. We studied the effects of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-modulating pathways on glucose- and succinate-stimulated insulin secretion and proinsulin biosynthesis in the rat and the insulin-resistant Psammomys obesus. Disruption of the anaplerotic pyruvate/malate shuttle by phenylacetic acid inhibited glucose- and succinate-stimulated insulin secretion and succinate-stimulated proinsulin biosynthesis in both species. In contrast, phenylacetic acid failed to inhibit glucose-stimulated proinsulin biosynthesis in P. obesus islets. Inhibition of the NADPH-consuming enzyme neuronal nitric oxide synthase (nNOS) with l-N(G)-nitro-l-arginine methyl ester or with N(G)-monomethyl-l-arginine(G) doubled succinate-stimulated insulin secretion in rat islets, suggesting that succinate- and nNOS-derived signals interact to regulate insulin secretion. In contrast, nNOS inhibition had no effect on succinate-stimulated proinsulin biosynthesis in both species. In P. obesus islets, insulin secretion was not stimulated by succinate in the absence of glucose, whereas proinsulin biosynthesis was increased 5-fold. Conversely, under stimulating glucose levels, succinate doubled insulin secretion, indicating glucose-dependence. Pyruvate ester and inhibition of nNOS partially mimicked the permissive effect of glucose on succinate-stimulated insulin secretion, suggesting that anaplerosis-derived signals render the beta-cells responsive to succinate. We conclude that beta-cell anaplerosis via pyruvate carboxylase is important for glucose- and succinate-stimulated insulin secretion and for succinate-stimulated proinsulin biosynthesis. In P. obesus, pyruvate/malate shuttle dependent and independent pathways that regulate proinsulin biosynthesis coexist; the latter can maintain fuel stimulated biosynthetic activity when the succinate-dependent pathway is inhibited. nNOS signaling is a negative regulator

  12. Interactions between imidazoline compounds and sulphonylureas in the regulation of insulin secretion

    PubMed Central

    Mourtada, Mirna; Brown, Colin A; Smith, Stephen A; Piercy, Valerie; Chan, Susan L F; Morgan, Noel G

    1997-01-01

    Imidazoline α2-antagonist drugs such as efaroxan have been shown to increase the insulin secretory response to sulphonylureas from rat pancreatic B-cells. We have investigated whether this reflects binding to an islet imidazoline receptor or whether α2-adrenoceptor antagonism is involved. Administration of (±)-efaroxan or glibenclamide to Wistar rats was associated with a transient increase in plasma insulin. When both drugs were administered together, the resultant increase in insulin levels was much greater than that obtained with either drug alone. Use of the resolved enantiomers of efaroxan revealed that the ability of the compound to enhance the insulin secretory response to glibenclamide resided only in the α2-selective-(+)-enantiomer; the imidazoline receptor-selective-(−)-enantiomer was ineffective. In vitro, (+)-efaroxan increased the insulin secretory response to glibenclamide in rat freshly isolated and cultured islets of Langerhans, whereas (−)-efaroxan was inactive. By contrast, (+)-efaroxan did not potentiate glucose-induced insulin secretion but (−)-efaroxan induced a marked increase in insulin secretion from islets incubated in the presence of 6 mM glucose. Incubation of rat islets under conditions designed to minimize the extent of α2-adrenoceptor signalling (by receptor blockade with phenoxybenzamine; receptor down-regulation or treatment with pertussis toxin) abolished the capacity of (+)-and (±)-efaroxan to enhance the insulin secretory response to glibenclamide. However, these manoeuvres did not alter the ability of (±)-efaroxan to potentiate glucose-induced insulin secretion. The results indicate that the enantiomers of efaroxan exert differential effects on insulin secretion which may result from binding to effector sites having opposite stereoselectivity. Binding of (−)-efaroxan (presumably to imidazoline receptors) results in potentiation of glucose-induced insulin secretion, whereas interaction of (+)-efaroxan with a

  13. Secretagogin affects insulin secretion in pancreatic β-cells by regulating actin dynamics and focal adhesion

    PubMed Central

    Yang, Seo-Yun; Lee, Jae-Jin; Lee, Jin-Hee; Lee, Kyungeun; Oh, Seung Hoon; Lim, Yu-Mi; Lee, Myung-Shik; Lee, Kong-Joo

    2016-01-01

    Secretagogin (SCGN), a Ca2+-binding protein having six EF-hands, is selectively expressed in pancreatic β-cells and neuroendocrine cells. Previous studies suggested that SCGN enhances insulin secretion by functioning as a Ca2+-sensor protein, but the underlying mechanism has not been elucidated. The present study explored the mechanism by which SCGN enhances glucose-induced insulin secretion in NIT-1 insulinoma cells. To determine whether SCGN influences the first or second phase of insulin secretion, we examined how SCGN affects the kinetics of insulin secretion in NIT-1 cells. We found that silencing SCGN suppressed the second phase of insulin secretion induced by glucose and H2O2, but not the first phase induced by KCl stimulation. Recruitment of insulin granules in the second phase of insulin secretion was significantly impaired by knocking down SCGN in NIT-1 cells. In addition, we found that SCGN interacts with the actin cytoskeleton in the plasma membrane and regulates actin remodelling in a glucose-dependent manner. Since actin dynamics are known to regulate focal adhesion, a critical step in the second phase of insulin secretion, we examined the effect of silencing SCGN on focal adhesion molecules, including FAK (focal adhesion kinase) and paxillin, and the cell survival molecules ERK1/2 (extracellular-signal-regulated kinase 1/2) and Akt. We found that glucose- and H2O2-induced activation of FAK, paxillin, ERK1/2 and Akt was significantly blocked by silencing SCGN. We conclude that SCGN controls glucose-stimulated insulin secretion and thus may be useful in the therapy of Type 2 diabetes. PMID:27095850

  14. The mechanisms of insulin secretion and calcium signaling in pancreatic β-cells exposed to fluoroquinolones.

    PubMed

    Bito, Motoki; Tomita, Takashi; Komori, Mika; Taogoshi, Takanori; Kimura, Yasuhiro; Kihira, Kenji

    2013-01-01

    Fluoroquinolones reportedly induce hypoglycemia through stimulation of insulin secretion from pancreatic β-cells via inhibition of K(ATP) channels and activation of L-type voltage-dependent Ca(2+) channels. In physiological condition, the cytosolic Ca(2+) concentration ([Ca(2+)](c)) is also regulated by release of Ca(2+) from intracellular Ca(2+) stores. In this study, we investigated the mechanism of insulin secretion induced by fluoroquinolones, with respect to intracellular Ca(2+) stores. Even where the absence of supplemental extracellular Ca(2+), insulin secretion and [Ca(2+)](c) were increased by gatifloxacin, levofloxacin or tolbutamide. Insulin secretion and the rise of [Ca(2+)](c) induced by fluoroquinolones were reduced by depleting of Ca(2+) in endoplasmic reticumum (ER) by thapsigargin, and inhibiting ryanodine receptor of ER by dantrolene. Inhibition of inositol 1,4,5-triphosphate receptor of ER by xestospongin C suppressed insulin secretion induced by fluoroquinolones, whereas it did not affect [Ca(2+)](c). Destruction of acidic Ca(2+) stores such as lysosome and lysosome-related organelles by glycyl-L-phenylalanine-2-nephthylamide (GPN) did not affect insulin secretion and the rise of [Ca(2+)](c) induced by fluoroquinolones. The increase in insulin and [Ca(2+)](c) induced by tolbutamide were reduced by thapsigargin, dantrolene, and GPN but not by xestospongin C. In conclusion, fluoroquinolones induces Ca(2+) release from ER mediated by the ryanodine receptor, and the reaction might involve in insulin secretion. Sulfonylureas induce Ca(2+) release from GPN-sensitive acidic Ca(2+) stores, but fluoroquinolones did not.

  15. Microbial phenolic metabolites improve glucose-stimulated insulin secretion and protect pancreatic beta cells against tert-butyl hydroperoxide-induced toxicity via ERKs and PKC pathways.

    PubMed

    Fernández-Millán, Elisa; Ramos, Sonia; Alvarez, Carmen; Bravo, Laura; Goya, Luis; Martín, María Ángeles

    2014-04-01

    Oxidative stress is accepted as one of the causes of beta cell failure in type 2 diabetes. Therefore, identification of natural antioxidant agents that preserve beta cell mass and function is considered an interesting strategy to prevent or treat diabetes. Recent evidences indicated that colonic metabolites derived from flavonoids could possess beneficial effects on various tissues. The aim of this work was to establish the potential anti-diabetic properties of the microbial-derived flavonoid metabolites 3,4-dihydroxyphenylacetic acid (DHPAA), 2,3-dihydroxybenzoic acid (DHBA) and 3-hydroxyphenylpropionic acid (HPPA). To this end, we tested their ability to influence beta cell function and to protect against tert-butyl hydroperoxide-induced beta cell toxicity. DHPAA and HPPA were able to potentiate glucose-stimulated insulin secretion (GSIS) in a beta cell line INS-1E and in rat pancreatic islets. Moreover, pre-treatment of cells with both compounds protected against beta cell dysfunction and death induced by the pro-oxidant. Finally, experiments with pharmacological inhibitors indicate that these effects were mediated by the activation of protein kinase C and the extracellular regulated kinases pathways. Altogether, these findings strongly suggest that the microbial-derived flavonoid metabolites DHPAA and HPPA may have anti-diabetic potential by promoting survival and function of pancreatic beta cells. Copyright © 2014 Elsevier Ltd. All rights reserved.

  16. Insulin secretion from beta cells within intact islets: location matters.

    PubMed

    Hoang Do, Oanh; Thorn, Peter

    2015-04-01

    The control of hormone secretion is central to body homeostasis, and its dysfunction is important in many diseases. The key cellular steps that lead to hormone secretion have been identified, and the stimulus-secretion pathway is understood in outline for many endocrine cells. In the case of insulin secretion from pancreatic beta cells, this pathway involves the uptake of glucose, cell depolarization, calcium entry, and the triggering of the fusion of insulin-containing granules with the cell membrane. The wealth of information on the control of insulin secretion has largely been obtained from isolated single-cell studies. However, physiologically, beta cells exist within the islets of Langerhans, with structural and functional specializations that are not preserved in single-cell cultures. This review focuses on recent work that is revealing distinct aspects of insulin secretion from beta cells within the islet.

  17. Nutrient-stimulated insulin secretion in mouse islets is critically dependent on intracellular pH

    PubMed Central

    Gunawardana, Subhadra C; Rocheleau, Jonathan V; Head, W Steven; Piston, David W

    2004-01-01

    Background Many mechanistic steps underlying nutrient-stimulated insulin secretion (NSIS) are poorly understood. The influence of intracellular pH (pHi) on insulin secretion is widely documented, and can be used as an investigative tool. This study demonstrates previously unknown effects of pHi-alteration on insulin secretion in mouse islets, which may be utilized to correct defects in insulin secretion. Methods Different components of insulin secretion in mouse islets were monitored in the presence and absence of forced changes in pHi. The parameters measured included time-dependent potentiation of insulin secretion by glucose, and direct insulin secretion by different mitochondrial and non-mitochondrial secretagogues. Islet pHi was altered using amiloride, removal of medium Cl-, and changing medium pH. Resulting changes in islet pHi were monitored by confocal microscopy using a pH-sensitive fluorescent indicator. To investigate the underlying mechanisms of the effects of pHi-alteration, cellular NAD(P)H levels were measured using two-photon excitation microscopy (TPEM). Data were analyzed using Student's t test. Results Time-dependent potentiation, a function normally absent in mouse islets, can be unmasked by a forced decrease in pHi. The optimal range of pHi for NSIS is 6.4–6.8. Bringing islet pHi to this range enhances insulin secretion by all mitochondrial fuels tested, reverses the inhibition of glucose-stimulated insulin secretion (GSIS) by mitochondrial inhibitors, and is associated with increased levels of cellular NAD(P)H. Conclusions Pharmacological alteration of pHi is a potential means to correct the secretory defect in non-insulin dependent diabetes mellitus (NIDDM), since forcing islet pHi to the optimal range enhances NSIS and induces secretory functions that are normally absent. PMID:15193158

  18. Glucose-induced cytosolic pH changes in beta-cells and insulin secretion are not causally related: studies in islets lacking the Na+/H+ exchangeR NHE1.

    PubMed

    Stiernet, Patrick; Nenquin, Myriam; Moulin, Pierre; Jonas, Jean-Christophe; Henquin, Jean-Claude

    2007-08-24

    The contribution of Na(+)/H(+) exchange (achieved by NHE proteins) to the regulation of beta-cell cytosolic pH(c), and the role of pH(c) changes in glucose-induced insulin secretion are disputed and were examined here. Using real-time PCR, we identified plasmalemmal NHE1 and intracellular NHE7 as the two most abundant NHE isoforms in mouse islets. We, therefore, compared insulin secretion, cytosolic free Ca(2+) ([Ca(2+)](c)) and pH(c) in islets from normal mice and mice bearing an inactivating mutation of NHE1 (Slc9A1-swe/swe). The experiments were performed in HCO(-)(3)/CO(2) or HEPES/NaOH buffers. PCR and functional approaches showed that NHE1 mutant islets do not express compensatory pH-regulating mechanisms. NHE1 played a greater role than HCO(-)(3)-dependent mechanisms in the correction of an acidification imposed by a pulse of NH(4)Cl. In contrast, basal pH(c) (in low glucose) and the alkalinization produced by high glucose were independent of NHE1. Dimethylamiloride, a classic blocker of Na(+)/H(+) exchange, did not affect pH(c) but increased insulin secretion in NHE1 mutant islets, indicating unspecific effects. In control islets, glucose similarly increased [Ca(2+)](c) and insulin secretion in HCO(-)(3) and HEPES buffer, although pH(c) changed in opposite directions. The amplification of insulin secretion that glucose produces when [Ca(2+)](c) is clamped at an elevated level by KCl was also unrelated to pH(c) and pH(c) changes. All effects of glucose on [Ca(2+)](c) and insulin secretion proved independent of NHE1. In conclusion, NHE1 protects beta-cells against strong acidification, but has no role in stimulus-secretion coupling. The changes in pH(c) produced by glucose involve HCO(-)(3)-dependent mechanisms. Variations in beta-cell pH(c) are not causally related to changes in insulin secretion.

  19. Palmitic acid-rich diet suppresses glucose-stimulated insulin secretion (GSIS) and induces endoplasmic reticulum (ER) stress in pancreatic islets in mice.

    PubMed

    Hirata, Takumi; Kawai, Toshihide; Hirose, Hiroshi; Tanaka, Kumiko; Kurosawa, Hideaki; Fujii, Chikako; Fujita, Haruhisa; Seto, Yoshiko; Matsumoto, Hideo; Itoh, Hiroshi

    2016-01-01

    The objective was to clarify whether dietary palmitic acid supplementation affects glucose-stimulated insulin secretion (GSIS) and the endoplasmic reticulum (ER) stress pathway in pancreatic islets in mice. Eight-week-old male C57BL/6J mice were randomly divided into three treatment diet groups: control diet, palmitic acid-supplemented diet (PAL) and oleic acid-supplemented diet (OLE). After 2 weeks of treatment, intraperitoneal glucose tolerance test and intraperitoneal insulin tolerance test were performed. GSIS was assessed by pancreatic perfusion in situ with basal (100 mg/dL) glucose followed by a high (300 mg/dL) glucose concentration. We measured mRNA levels of ER stress markers such as C/EBP homologous protein (CHOP), immunoglobulin heavy-chain binding protein (BIP) and X-box binding protein (XBP)-1 using real-time polymerase chain reaction (PCR) analyses in isolated islets. Immunohistochemical staining was also performed. Mice fed PAL showed significantly decreased glucose tolerance (p < 0.05). In the perfusion study, GSIS was significantly suppressed in the PAL group (p < 0.05). Semi-quantitative RT-PCR revealed that islet CHOP, BIP, and XBP-1 mRNA expression were significantly increased in the PAL group (p < 0.05). TUNEL-positive β-cells were not detected in all groups. Dietary palmitic acid-supplementation for 2 weeks might suppress GSIS and induce ER stress in pancreatic islets in mice, in the early stage of lipotoxicity.

  20. Baccharis dracunculifolia methanol extract enhances glucose-stimulated insulin secretion in pancreatic islets of monosodium glutamate induced-obesity model rats.

    PubMed

    Hocayen, Palloma de A S; Grassiolli, Sabrina; Leite, Nayara C; Pochapski, Márcia T; Pereira, Ricardo A; da Silva, Luiz A; Snack, Andre L; Michel, R Garcia; Kagimura, Francini Y; da Cunha, Mário A A; Malfatti, Carlos R M

    2016-07-01

    Obesity is the main risk factor for type 2 diabetes mellitus. Secondary metabolites with biological activities and pharmacological potential have been identified in species of the Baccharis genus that are specifically distributed in the Americas. This study evaluated the effects of methanol extracts from Baccharis dracunculifolia DC. Asteraceae on metabolic parameters, satiety, and growth in monosodium glutamate (MSG) induced-obesity model rats. MSG was administered to 32 newborn rats (4 mg/g of body weight) once daily for 5 consecutive days. Four experimental groups (control, control + extract, MSG, and MSG + extract) were treated for 30 consecutive days with 400 mg/kg of B. dracunculifolia extract by gavage. Biochemical parameters, antioxidant activity, total extract phenolic content (methanolic, ethanolic, and acetone extractions), and pancreatic islets were evaluated. High levels of phenolic compounds were identified in B. dracunculifolia extracts (methanol: 46.2 ± 0.4 mg GAE/L; acetate: 70.5 ± 0.5 mg GAE/L; and ethanol: 30.3 ± 0.21 mg GAE/L); high antioxidant activity was detected in B. dracunculifolia ethanol and methanol extracts. The concentration of serum insulin increased 30% in obese animals treated with extract solutions (1.4-2.0 µU/mL, p < 0.05). Insulin secretion in pancreatic islets was 8.3 mM glucose (58%, p < 0.05) and 16.7 mM (99.5%, p < 0.05) in rats in the MSG + extract and MSG groups, respectively. Treatment with B. dracunculifolia extracts protected pancreatic islets and prevented the irreversible cellular damage observed in animals in obesity and diabetes models.

  1. Role for the TRPV1 channel in insulin secretion from pancreatic beta cells.

    PubMed

    Diaz-Garcia, Carlos Manlio; Morales-Lázaro, Sara L; Sánchez-Soto, Carmen; Velasco, Myrian; Rosenbaum, Tamara; Hiriart, Marcia

    2014-06-01

    Transient receptor potential channels have been put forward as regulators of insulin secretion. A role for the TRPV1 ion channel in insulin secretion has been suggested in pancreatic beta cell lines. We explored whether TRPV1 is functionally expressed in RINm5F and primary beta cells from neonate and adult rats. We examined if capsaicin could activate cationic non-selective currents. Our results show that TRPV1 channels are not functional in insulin-secreting cells, since capsaicin did not produce current activation, not even under culture conditions known to induce the expression of other ion channels in these cells. Although TRPV1 channels seem to be irrelevant for the physiology of isolated beta cells, they may play a role in glucose homeostasis acting through the nerve fibers that regulate islet function. At the physiological level, we observed that Trpv1 (-/-) mice presented lower fasting insulin levels than their wild-type littermates, however, we did not find differences between these experimental groups nor in the glucose tolerance test or in the insulin secretion. However, we did find that the Trpv1 (-/-) mice exhibited a higher insulin sensitivity compared to their wild-type counterparts. Our results demonstrate that TRPV1 does not contribute to glucose-induced insulin secretion in beta cells as was previously thought, but it is possible that it may control insulin sensitivity.

  2. Endocrine Determinants of Changes in Insulin Sensitivity and Insulin Secretion during a Weight Cycle in Healthy Men

    PubMed Central

    Karschin, Judith; Lagerpusch, Merit; Enderle, Janna; Eggeling, Ben; Müller, Manfred J.; Bosy-Westphal, Anja

    2015-01-01

    Objective Changes in insulin sensitivity (IS) and insulin secretion occur with perturbations in energy balance and glycemic load (GL) of the diet that may precede the development of insulin resistance and hyperinsulinemia. Determinants of changes in IS and insulin secretion with weight cycling in non-obese healthy subjects remain unclear. Methods In a 6wk controlled 2-stage randomized dietary intervention 32 healthy men (26±4y, BMI: 24±2kg/m2) followed 1wk of overfeeding (OF), 3wks of caloric restriction (CR) containing either 50% or 65% carbohydrate (CHO) and 2wks of refeeding (RF) with the same amount of CHO but either low or high glycaemic index at ±50% energy requirement. Measures of IS (basal: HOMA-index, postprandial: Matsuda-ISI), insulin secretion (early: Stumvoll-index, total: tAUC-insulin/tAUC-glucose) and potential endocrine determinants (ghrelin, leptin, adiponectin, thyroid hormone levels, 24h-urinary catecholamine excretion) were assessed. Results IS improved and insulin secretion decreased due to CR and normalized upon RF. Weight loss-induced improvements in basal and postprandial IS were associated with decreases in leptin and increases in ghrelin levels, respectively (r = 0.36 and r = 0.62, p<0.05). Weight regain-induced decrease in postprandial IS correlated with increases in adiponectin, fT3, TSH, GL of the diet and a decrease in ghrelin levels (r-values between -0.40 and 0.83, p<0.05) whereas increases in early and total insulin secretion were associated with a decrease in leptin/adiponectin-ratio (r = -0.52 and r = -0.46, p<0.05) and a decrease in fT4 (r = -0.38, p<0.05 for total insulin secretion only). After controlling for GL associations between RF-induced decrease in postprandial IS and increases in fT3 and TSH levels were no longer significant. Conclusion Weight cycling induced changes in IS and insulin secretion were associated with changes in all measured hormones, except for catecholamine excretion. While leptin, adiponectin and

  3. Activation of islet 5-HT4 receptor regulates glycemic control through promoting insulin secretion.

    PubMed

    Chen, Hui; Hong, Feng; Chen, Ye; Li, Ji; Yao, Yuan-Sheng; Zhang, Yue; Zheng, Li-Fei; Zhu, Jin-Xia

    2016-10-15

    Mosapride, a gastrointestinal prokinetic drug, is an agonist of 5-hydroxytryptamine (5-HT) receptor 4 that also reduces blood glucose. Whether 5-HT4 receptor is distributed in pancreatic islets and whether mosapride can directly stimulate insulin secretion is unclear. In the present study, the protein expression and cellular location of 5-HT4 receptor in pancreas was detected through western blotting and immunofluorescence. The acute effects of 5-HT4 receptor agonists, mosapride and prucalopride, on insulin secretion were investigated in vivo and in vitro in normal and alloxan-induced diabetes rats. The results indicated that 5-HT4 receptor immunoreactivity was co-existed in the islets insulin-immunoreactive cells of rat, mouse, pig and human. However the immunoreactive cells of insulin and 5-HT4 receptor and the protein expression of 5-HT4 receptor were significantly decreased in the pancreas of alloxan-induced diabetes rats. In normal rats, mosapride and prucalopride decreased blood glucose and increased insulin secretion during glucose tolerance test, in association with an increase in glucose-stimulated insulin secretion, which was abolished by the 5-HT4 receptor antagonist GR113808. In diabetes rats, mosapride and prucalopride failed to improve blood glucose and insulin levels in the group of 180mg/kg alloxan, but increased glucose-stimulated insulin secretion in the group of 120mg/kg alloxan in vitro. We conclude that 5-HT4 receptor is distributed in the islet β cell. Activation of 5-HT4 receptor is able to stimulate insulin secretion directly, thereby reduce blood glucose. The study provides important experimental evidences for the 5-HT4 receptor regulating insulin secretion and acting as a potential drug target in diabetes treatment. Copyright © 2016 Elsevier B.V. All rights reserved.

  4. Insulin secretion stimulated by allogeneic lymphocytes in an inbred strain of mice.

    PubMed Central

    García, J B; Venturino, M C; Alvarez, E; Fabiano de Bruno, L; Braun, M; Pivetta, O H; Basabe, J C

    1986-01-01

    Effects of intraperitoneal injection of allogeneic lymphocytes on insulin secretion were studied in incubated pancreas slices from BALB/c mice. Injection of allogeneic lymphocytes from C57BL/6J (H2b) mice increased insulin secretion, both in basal and 11-mM glucose-stimulated conditions. This effect was only present when at least 5 X 10(6) or 1 X 10(6) cells were injected (in basal and stimulated conditions, respectively). Glucose-induced insulin secretion (3.3-27.5 mM) was significantly increased in pancreata from mice injected with allogeneic lymphocytes. No effect was observed when glucose was not included in the incubation medium. Intraperitoneal injection of Dextran 70 produced no change in glucose-elicited insulin secretion. There were no differences in glucagon and somatostatin (SRIF) secretion obtained from pancreas of mice injected with allogeneic or syngeneic lymphocytes. Injection of allogeneic cells increases insulin secretion (basal and both phases of 11 mM glucose-stimulated secretion). Puromycin significantly inhibited the second phase of insulin secretion. These results suggest that: Injection of allogeneic lymphocytes raises both basal and glucose-stimulated insulin secretion. This effect seems to be connected with the major histocompatibility complex, and to be related to the number of allogeneic cells injected. Injection of allogeneic lymphocytes seems to sensitize the beta cell response to glucose stimulus. Neither glucagon nor SRIF secretion are altered by alloantigen injection. The stimulatory effect of allogeneic lymphocytes is related, at least in part, to insulin synthesis. PMID:2871044

  5. Regulation of Insulin Synthesis and Secretion and Pancreatic Beta-Cell Dysfunction in Diabetes

    PubMed Central

    Fu, Zhuo; Gilbert, Elizabeth R.; Liu, Dongmin

    2014-01-01

    Pancreatic β-cell dysfunction plays an important role in the pathogenesis of both type 1 and type 2 diabetes. Insulin, which is produced in β-cells, is a critical regulator of metabolism. Insulin is synthesized as preproinsulin and processed to proinsulin. Proinsulin is then converted to insulin and C-peptide and stored in secretary granules awaiting release on demand. Insulin synthesis is regulated at both the transcriptional and translational level. The cis-acting sequences within the 5′ flanking region and trans-activators including paired box gene 6 (PAX6), pancreatic and duodenal homeobox-1(PDX-1), MafA, and B-2/Neurogenic differentiation 1 (NeuroD1) regulate insulin transcription, while the stability of preproinsulin mRNA and its untranslated regions control protein translation. Insulin secretion involves a sequence of events in β-cells that lead to fusion of secretory granules with the plasma membrane. Insulin is secreted primarily in response to glucose, while other nutrients such as free fatty acids and amino acids can augment glucose-induced insulin secretion. In addition, various hormones, such as melatonin, estrogen, leptin, growth hormone, and glucagon like peptide-1 also regulate insulin secretion. Thus, the β-cell is a metabolic hub in the body, connecting nutrient metabolism and the endocrine system. Although an increase in intracellular [Ca2+] is the primary insulin secretary signal, cAMP signaling-dependent mechanisms are also critical in the regulation of insulin secretion. This article reviews current knowledge on how β-cells synthesize and secrete insulin. In addition, this review presents evidence that genetic and environmental factors can lead to hyperglycemia, dyslipidemia, inflammation, and autoimmunity, resulting in β-cell dysfunction, thereby triggering the pathogenesis of diabetes. PMID:22974359

  6. Regulation of Insulin Secretion by Phosphatidylinositol-4,5-Bisphosphate

    PubMed Central

    Tomas, Alejandra; Yermen, Barbara; Regazzi, Romano; Pessin, Jeffrey E.; Halban, Philippe A.

    2014-01-01

    The role of PIP2 in pancreatic beta cell function was examined here using the beta cell line MIN6B1. Blocking PIP2 with PH-PLC-GFP or PIP5KIγ RNAi did not impact on glucose-stimulated secretion although susceptibility to apoptosis was increased. Over-expression of PIP5KIγ improved cell survival and inhibited secretion with accumulation of endocytic vacuoles containing F-actin, PIP2, transferrin receptor, caveolin 1, Arf6 and the insulin granule membrane protein phogrin but not insulin. Expression of constitutively active Arf6 Q67L also resulted in vacuole formation and inhibition of secretion, which was reversed by PH-PLC-GFP co-expression. PIP2 co-localized with gelsolin and F-actin, and gelsolin co-expression partially reversed the secretory defect of PIP5KIγ-over-expressing cells. RhoA/ROCK inhibition increased actin depolymerization and secretion, which was prevented by over-expressing PIP5KIγ, while blocking PIP2 reduced constitutively active RhoA V14-induced F-actin polymerization. In conclusion, although PIP2 plays a pro-survival role in MIN6B1 cells, excessive PIP2 production due to PIP5KIγ over-expression inhibits secretion due to both a defective Arf6/PIP5KIγ-dependent endocytic recycling of secretory membrane and secretory membrane components such as phogrin and the RhoA/ROCK/PIP5KIγ-dependent perturbation of F-actin cytoskeleton remodeling. PMID:19845918

  7. Increased adiposity and insulin correlates with the progressive suppression of pulsatile GH secretion during weight gain.

    PubMed

    Steyn, F J; Xie, T Y; Huang, L; Ngo, S T; Veldhuis, J D; Waters, M J; Chen, C

    2013-01-01

    Pathological changes associated with obesity are thought to contribute to GH deficiency. However, recent observations suggest that impaired GH secretion relative to excess calorie consumption contributes to progressive weight gain and thus may contribute to the development of obesity. To clarify this association between adiposity and GH secretion, we investigated the relationship between pulsatile GH secretion and body weight; epididymal fat mass; and circulating levels of leptin, insulin, non-esterified free fatty acids (NEFAs), and glucose. Data were obtained from male mice maintained on a standard or high-fat diet. We confirm the suppression of pulsatile GH secretion following dietary-induced weight gain. Correlation analyses reveal an inverse relationship between measures of pulsatile GH secretion, body weight, and epididymal fat mass. Moreover, we demonstrate an inverse relationship between measures of pulsatile GH secretion and circulating levels of leptin and insulin. The secretion of GH did not change relative to circulating levels of NEFAs or glucose. We conclude that impaired pulsatile GH secretion in the mouse occurs alongside progressive weight gain and thus precedes the development of obesity. Moreover, data illustrate key interactions between GH secretion and circulating levels of insulin and reflect the potential physiological role of GH in modulation of insulin-induced lipogenesis throughout positive energy balance.

  8. Urea impairs β cell glycolysis and insulin secretion in chronic kidney disease

    PubMed Central

    Koppe, Laetitia; Nyam, Elsa; Vivot, Kevin; Manning Fox, Jocelyn E.; Dai, Xiao-Qing; Nguyen, Bich N.; Attané, Camille; Moullé, Valentine S.; MacDonald, Patrick E.; Ghislain, Julien

    2016-01-01

    Disorders of glucose homeostasis are common in chronic kidney disease (CKD) and are associated with increased mortality, but the mechanisms of impaired insulin secretion in this disease remain unclear. Here, we tested the hypothesis that defective insulin secretion in CKD is caused by a direct effect of urea on pancreatic β cells. In a murine model in which CKD is induced by 5/6 nephrectomy (CKD mice), we observed defects in glucose-stimulated insulin secretion in vivo and in isolated islets. Similarly, insulin secretion was impaired in normal mouse and human islets that were cultured with disease-relevant concentrations of urea and in islets from normal mice treated orally with urea for 3 weeks. In CKD mouse islets as well as urea-exposed normal islets, we observed an increase in oxidative stress and protein O-GlcNAcylation. Protein O-GlcNAcylation was also observed in pancreatic sections from CKD patients. Impairment of insulin secretion in both CKD mouse and urea-exposed islets was associated with reduced glucose utilization and activity of phosphofructokinase 1 (PFK-1), which could be reversed by inhibiting O-GlcNAcylation. Inhibition of O-GlcNAcylation also restored insulin secretion in both mouse models. These results suggest that insulin secretory defects associated with CKD arise from elevated circulating levels of urea that increase islet protein O-GlcNAcylation and impair glycolysis. PMID:27525435

  9. Urea impairs β cell glycolysis and insulin secretion in chronic kidney disease.

    PubMed

    Koppe, Laetitia; Nyam, Elsa; Vivot, Kevin; Manning Fox, Jocelyn E; Dai, Xiao-Qing; Nguyen, Bich N; Trudel, Dominique; Attané, Camille; Moullé, Valentine S; MacDonald, Patrick E; Ghislain, Julien; Poitout, Vincent

    2016-09-01

    Disorders of glucose homeostasis are common in chronic kidney disease (CKD) and are associated with increased mortality, but the mechanisms of impaired insulin secretion in this disease remain unclear. Here, we tested the hypothesis that defective insulin secretion in CKD is caused by a direct effect of urea on pancreatic β cells. In a murine model in which CKD is induced by 5/6 nephrectomy (CKD mice), we observed defects in glucose-stimulated insulin secretion in vivo and in isolated islets. Similarly, insulin secretion was impaired in normal mouse and human islets that were cultured with disease-relevant concentrations of urea and in islets from normal mice treated orally with urea for 3 weeks. In CKD mouse islets as well as urea-exposed normal islets, we observed an increase in oxidative stress and protein O-GlcNAcylation. Protein O-GlcNAcylation was also observed in pancreatic sections from CKD patients. Impairment of insulin secretion in both CKD mouse and urea-exposed islets was associated with reduced glucose utilization and activity of phosphofructokinase 1 (PFK-1), which could be reversed by inhibiting O-GlcNAcylation. Inhibition of O-GlcNAcylation also restored insulin secretion in both mouse models. These results suggest that insulin secretory defects associated with CKD arise from elevated circulating levels of urea that increase islet protein O-GlcNAcylation and impair glycolysis.

  10. Important role of heparan sulfate in postnatal islet growth and insulin secretion

    SciTech Connect

    Takahashi, Iwao; Noguchi, Naoya; Nata, Koji; Yamada, Shuhei; Kaneiwa, Tomoyuki; Mizumoto, Shuji; Ikeda, Takayuki; Sugihara, Kazushi; Asano, Masahide; Yoshikawa, Takeo; Yamauchi, Akiyo; Shervani, Nausheen Jamal; Uruno, Akira; Kato, Ichiro; Unno, Michiaki; Sugahara, Kazuyuki; Takasawa, Shin; and others

    2009-05-22

    Heparan sulfate (HS) binds with several signaling molecules and regulates ligand-receptor interactions, playing an essential role in embryonic development. Here we showed that HS was intensively expressed in pancreatic islet {beta}-cells after 1 week of age in mice. The enzymatic removal of HS in isolated islets resulted in attenuated glucose-induced insulin secretion with a concomitant reduction in gene expression of several key components in the insulin secretion machinery. We further depleted islet HS by inactivating the exostosin tumor-like 3 gene specifically in {beta}-cells. These mice exhibited abnormal islet morphology with reduced {beta}-cell proliferation after 1 week of age and glucose intolerance due to defective insulin secretion. These results demonstrate that islet HS is involved in the regulation of postnatal islet maturation and required to ensure normal insulin secretion.

  11. CART is overexpressed in human type 2 diabetic islets and inhibits glucagon secretion and increases insulin secretion.

    PubMed

    Abels, Mia; Riva, Matteo; Bennet, Hedvig; Ahlqvist, Emma; Dyachok, Oleg; Nagaraj, Vini; Shcherbina, Liliya; Fred, Rikard G; Poon, Wenny; Sörhede-Winzell, Maria; Fadista, Joao; Lindqvist, Andreas; Kask, Lena; Sathanoori, Ramasri; Dekker-Nitert, Marloes; Kuhar, Michael J; Ahrén, Bo; Wollheim, Claes B; Hansson, Ola; Tengholm, Anders; Fex, Malin; Renström, Erik; Groop, Leif; Lyssenko, Valeriya; Wierup, Nils

    2016-09-01

    Insufficient insulin release and hyperglucagonaemia are culprits in type 2 diabetes. Cocaine- and amphetamine-regulated transcript (CART, encoded by Cartpt) affects islet hormone secretion and beta cell survival in vitro in rats, and Cart (-/-) mice have diminished insulin secretion. We aimed to test if CART is differentially regulated in human type 2 diabetic islets and if CART affects insulin and glucagon secretion in vitro in humans and in vivo in mice. CART expression was assessed in human type 2 diabetic and non-diabetic control pancreases and rodent models of diabetes. Insulin and glucagon secretion was examined in isolated islets and in vivo in mice. Ca(2+) oscillation patterns and exocytosis were studied in mouse islets. We report an important role of CART in human islet function and glucose homeostasis in mice. CART was found to be expressed in human alpha and beta cells and in a subpopulation of mouse beta cells. Notably, CART expression was several fold higher in islets of type 2 diabetic humans and rodents. CART increased insulin secretion in vivo in mice and in human and mouse islets. Furthermore, CART increased beta cell exocytosis, altered the glucose-induced Ca(2+) signalling pattern in mouse islets from fast to slow oscillations and improved synchronisation of the oscillations between different islet regions. Finally, CART reduced glucagon secretion in human and mouse islets, as well as in vivo in mice via diminished alpha cell exocytosis. We conclude that CART is a regulator of glucose homeostasis and could play an important role in the pathophysiology of type 2 diabetes. Based on the ability of CART to increase insulin secretion and reduce glucagon secretion, CART-based agents could be a therapeutic modality in type 2 diabetes.

  12. Influence of Insulin in the Ventromedial Hypothalamus on Pancreatic Glucagon Secretion In Vivo

    PubMed Central

    Paranjape, Sachin A.; Chan, Owen; Zhu, Wanling; Horblitt, Adam M.; McNay, Ewan C.; Cresswell, James A.; Bogan, Jonathan S.; McCrimmon, Rory J.; Sherwin, Robert S.

    2010-01-01

    OBJECTIVE Insulin released by the β-cell is thought to act locally to regulate glucagon secretion. The possibility that insulin might also act centrally to modulate islet glucagon secretion has received little attention. RESEARCH DESIGN AND METHODS Initially the counterregulatory response to identical hypoglycemia was compared during intravenous insulin and phloridzin infusion in awake chronically catheterized nondiabetic rats. To explore whether the disparate glucagon responses seen were in part due to changes in ventromedial hypothalamus (VMH) exposure to insulin, bilateral guide cannulas were inserted to the level of the VMH and 8 days later rats received a VMH microinjection of either 1) anti-insulin affibody, 2) control affibody, 3) artificial extracellular fluid, 4) insulin (50 μU), 5) insulin receptor antagonist (S961), or 6) anti-insulin affibody plus a γ-aminobutyric acid A (GABAA) receptor agonist muscimol, prior to a hypoglycemic clamp or under baseline conditions. RESULTS As expected, insulin-induced hypoglycemia produced a threefold increase in plasma glucagon. However, the glucagon response was fourfold to fivefold greater when circulating insulin did not increase, despite equivalent hypoglycemia and C-peptide suppression. In contrast, epinephrine responses were not altered. The phloridzin-hypoglycemia induced glucagon increase was attenuated (40%) by VMH insulin microinjection. Conversely, local VMH blockade of insulin amplified glucagon twofold to threefold during insulin-induced hypoglycemia. Furthermore, local blockade of basal insulin levels or insulin receptors within the VMH caused an immediate twofold increase in fasting glucagon levels that was prevented by coinjection to the VMH of a GABAA receptor agonist. CONCLUSIONS Together, these data suggest that insulin's inhibitory effect on α-cell glucagon release is in part mediated at the level of the VMH under both normoglycemic and hypoglycemic conditions. PMID:20299468

  13. Restoration of insulin secretion in pancreatic islets of protein-deficient rats by reduced expression of insulin receptor substrate (IRS)-1 and IRS-2.

    PubMed

    Araujo, E P; Amaral, M E C; Filiputti, E; De Souza, C T; Laurito, T L; Augusto, V D; Saad, M J A; Boschero, A C; Velloso, L A; Carneiro, E M

    2004-04-01

    Autocrine and paracrine insulin signaling may participate in the fine control of insulin secretion. In the present study, tissue distribution and protein amounts of the insulin receptor and its major substrates, insulin receptor substrate (IRS)-1 and IRS-2, were evaluated in a model of impaired glucose-induced insulin secretion, the protein-deficient rat. Immunoblot and RT-PCR studies showed that the insulin receptor and IRS-2 expression are increased, whilst IRS-1 protein and mRNA contents are decreased in pancreatic islets of protein-deficient rats. Immunohistochemical studies revealed that the insulin receptor and IRS-1 and -2 are present in the great majority of islet cells; however, the greatest staining was localized at the periphery, suggesting a co-localization with non-insulin-secreting cells. Exogenous insulin stimulation of isolated islets promoted higher insulin receptor and IRS-1 and -2 tyrosine phosphorylation in islets from protein-deficient rats, as compared with controls. Moreover, insulin-induced IRS-1- and IRS-2-associated phosphatidylinositol 3-kinase activity are increased in islets of protein-deficient rats. The reduction of IRS-1 and IRS-2 protein expression in islets isolated from protein-deficient rats by the use of antisense IRS-1 or IRS-2 phosphorthioate-modified oligonucleotides partially restored glucose-induced insulin secretion. Thus, the impairment of insulin cell signaling through members of the IRS family of proteins in isolated rat pancreatic islets improves glucose-induced insulin secretion. The present data reinforced the role of insulin paracrine and autocrine signaling in the control of its own secretion.

  14. Structural and functional changes in human insulin induced by methylglyoxal.

    PubMed

    Jia, Xuming; Olson, Douglas J H; Ross, Andrew R S; Wu, Lingyun

    2006-07-01

    Elevated methylglyoxal (MG) levels have been reported in insulin-resistance syndrome. The present study investigated whether MG, a highly reactive metabolite of glucose, induced structural and functional changes of insulin. Incubation of human insulin with MG in vitro yielded MG-insulin adducts, as evidenced by additional peaks observed on mass spectrometric (MS) analysis of the incubates. Tandem MS analysis of insulin B-chain adducts confirmed attachment of MG at an arginine residue. [3H]-2-deoxyglucose uptake by 3T3-L1 adipocytes was significantly and concentration-dependently decreased after the treatment with MG-insulin adducts, in comparison with the effect of native insulin at the same concentrations. A significant decrease of glucose uptake induced by MG-insulin adducts was also observed in L8 skeletal muscle cells. MG alone had no effect on glucose uptake or the transcriptional expression of insulin receptor. Unlike native insulin, MG-insulin adducts did not inhibit insulin release from pancreatic beta-cells. The degradation of MG-insulin through liver cells was also decreased. In conclusion, MG modifies insulin by attaching to internal arginine residue in beta-chain of insulin. The formation of this MG-insulin adduct decreases insulin-mediated glucose uptake, impairs autocrine control of insulin secretion, and decreases insulin clearance. These structural and functional abnormalities of insulin molecule may contribute to the pathogenesis of insulin resistance.

  15. Simvastatin Impairs Insulin Secretion by Multiple Mechanisms in MIN6 Cells

    PubMed Central

    López Rodríguez, Maykel; Stančáková, Alena; Kuusisto, Johanna; Kokkola, Tarja; Laakso, Markku

    2015-01-01

    Statins are widely used in the treatment of hypercholesterolemia and are efficient in the prevention of cardiovascular disease. Molecular mechanisms explaining statin-induced impairment in insulin secretion remain largely unknown. In the current study, we show that simvastatin decreased glucose-stimulated insulin secretion in mouse pancreatic MIN6 β-cells by 59% and 79% (p<0.01) at glucose concentration of 5.5 mmol/l and 16.7 mmol/l, respectively, compared to control, whereas pravastatin did not impair insulin secretion. Simvastatin induced decrease in insulin secretion occurred through multiple targets. In addition to its established effects on ATP-sensitive potassium channels (p = 0.004) and voltage-gated calcium channels (p = 0.004), simvastatin suppressed insulin secretion stimulated by muscarinic M3 or GPR40 receptor agonists (Tak875 by 33%, p = 0.002; GW9508 by 77%, p = 0.01) at glucose level of 5.5 mmol/l, and inhibited calcium release from the endoplasmic reticulum. Impaired insulin secretion caused by simvastatin treatment were efficiently restored by GPR119 or GLP-1 receptor stimulation and by direct activation of cAMP-dependent signaling pathways with forskolin. The effects of simvastatin treatment on insulin secretion were not affected by the presence of hyperglycemia. Our observation of the opposite effects of simvastatin and pravastatin on glucose-stimulated insulin secretion is in agreement with previous reports showing that simvastatin, but not pravastatin, was associated with increased risk of incident diabetes. PMID:26561346

  16. ENPP1 Affects Insulin Action and Secretion: Evidences from In Vitro Studies

    PubMed Central

    Di Paola, Rosa; Caporarello, Nunzia; Marucci, Antonella; Dimatteo, Claudia; Iadicicco, Claudia; Del Guerra, Silvia; Prudente, Sabrina; Sudano, Dora; Miele, Claudia; Parrino, Cristina; Piro, Salvatore; Beguinot, Francesco; Marchetti, Piero

    2011-01-01

    The aim of this study was to deeper investigate the mechanisms through which ENPP1, a negative modulator of insulin receptor (IR) activation, plays a role on insulin signaling, insulin secretion and eventually glucose metabolism. ENPP1 cDNA (carrying either K121 or Q121 variant) was transfected in HepG2 liver-, L6 skeletal muscle- and INS1E beta-cells. Insulin-induced IR-autophosphorylation (HepG2, L6, INS1E), Akt-Ser473, ERK1/2-Thr202/Tyr204 and GSK3-beta Ser9 phosphorylation (HepG2, L6), PEPCK mRNA levels (HepG2) and 2-deoxy-D-glucose uptake (L6) was studied. GLUT 4 mRNA (L6), insulin secretion and caspase-3 activation (INS1E) were also investigated. Insulin-induced IR-autophosphorylation was decreased in HepG2-K, L6-K, INS1E-K (20%, 52% and 11% reduction vs. untransfected cells) and twice as much in HepG2-Q, L6-Q, INS1E-Q (44%, 92% and 30%). Similar data were obtained with Akt-Ser473, ERK1/2-Thr202/Tyr204 and GSK3-beta Ser9 in HepG2 and L6. Insulin-induced reduction of PEPCK mRNA was progressively lower in untransfected, HepG2-K and HepG2-Q cells (65%, 54%, 23%). Insulin-induced glucose uptake in untransfected L6 (60% increase over basal), was totally abolished in L6-K and L6-Q cells. GLUT 4 mRNA was slightly reduced in L6-K and twice as much in L6-Q (13% and 25% reduction vs. untransfected cells). Glucose-induced insulin secretion was 60% reduced in INS1E-K and almost abolished in INS1E-Q. Serum deficiency activated caspase-3 by two, three and four folds in untransfected INS1E, INS1E-K and INS1E-Q. Glyburide-induced insulin secretion was reduced by 50% in isolated human islets from homozygous QQ donors as compared to those from KK and KQ individuals. Our data clearly indicate that ENPP1, especially when the Q121 variant is operating, affects insulin signaling and glucose metabolism in skeletal muscle- and liver-cells and both function and survival of insulin secreting beta-cells, thus representing a strong pathogenic factor predisposing to insulin resistance

  17. Cellular communication and heterogeneity in pancreatic islet insulin secretion dynamics.

    PubMed

    Benninger, Richard K P; Piston, David W

    2014-08-01

    Coordinated pulses of electrical activity and insulin secretion are a hallmark of the islet of Langerhans. These coordinated behaviors are lost when β cells are dissociated, which also leads to increased insulin secretion at low glucose levels. Islets without gap junctions exhibit asynchronous electrical activity similar to dispersed cells, but their secretion at low glucose levels is still clamped off, putatively by a juxtacrine mechanism. Mice lacking β cell gap junctions have near-normal average insulin levels, but are glucose intolerant due to reduced first-phase and pulsatile insulin secretion, illustrating the importance of temporal dynamics. Here, we review the quantitative data on islet synchronization and the current mathematical models that have been developed to explain these behaviors and generate greater understanding of the underlying mechanisms. Copyright © 2014 Elsevier Ltd. All rights reserved.

  18. Cellular Communication and Heterogeneity in Pancreatic Islet Insulin Secretion Dynamics

    PubMed Central

    Benninger, Richard K.P.; Piston, David W.

    2014-01-01

    Coordinated pulses of electrical activity and insulin secretion are a hallmark of the islet of Langerhans. These coordinated behaviors are lost when β-cells are dissociated, which also leads to increased insulin secretion at low glucose. Islets without gap junctions exhibit asynchronous electrical activity similar to dispersed cells, but their secretion at low glucose is still clamped off, putatively by a juxtacrine mechanism. Mice lacking β-cell gap junctions have near-normal average insulin levels, but are glucose intolerant due to reduced first-phase and pulsatile insulin secretion, illustrating the importance of temporal dynamics. We review the quantitative data on islet synchronization and the current mathematical models that have been developed to explain these behaviors and generate greater understanding of the underlying mechanisms. PMID:24679927

  19. Insulin secretion and cellular glucose metabolism after prolonged low-grade intralipid infusion in young men.

    PubMed

    Jensen, Christine B; Storgaard, Heidi; Holst, Jens J; Dela, Flemming; Madsbad, Sten; Vaag, Allan A

    2003-06-01

    We examined the simultaneous effects of a 24-h low-grade Intralipid infusion on peripheral glucose disposal, intracellular glucose partitioning and insulin secretion rates in twenty young men, by 2-step hyperinsulinemic euglycemic clamp [low insulin clamp (LI), 10 mU/m(2) x min; high insulin clamp (HI), 40 mU/m(2) x min], 3-(3)H-glucose, indirect calorimetry, and iv glucose tolerance test. Free fatty acid concentrations were similar during basal steady state but 3.7- to 13-fold higher during clamps. P-glucagon increased and the insulin/glucagon ratio decreased at both LI and HI during Intralipid infusion. At LI, glucose oxidation decreased by 10%, whereas glucose disposal, glycolytic flux, glucose storage, and glucose production were not significantly altered. At HI, glucose disposal, and glucose oxidation decreased by 12% and 24%, respectively, during Intralipid infusion. Glycolytic flux, glucose storage, and glucose production were unchanged. Insulin secretion rates increased in response to Intralipid infusion, but disposition indices (DI = insulin action.insulin secretion) were unchanged. In conclusion, a 24-h low-grade Intralipid infusion caused insulin resistance in the oxidative (but not in the nonoxidative) glucose metabolism in young healthy men. Moreover, insulin hypersecretion perfectly countered the free-fatty acid-induced insulin resistance. Future studies are needed to determine the role of a prolonged moderate lipid load in subjects at increased risk of developing diabetes.

  20. Insulin secretion abnormalities in exocrine pancreatic sufficient cystic fibrosis patients.

    PubMed

    Wooldridge, Jamie L; Szczesniak, Rhonda D; Fenchel, Matthew C; Elder, Deborah A

    2015-11-01

    The aim of this study is to assess insulin secretion in pediatric cystic fibrosis (CF) patients with exocrine pancreatic sufficiency. Glucose and insulin responses during an oral glucose tolerance test (OGTT) were measured in 146 CF patients. Patients were divided into exocrine sufficient (CF-PS) and insufficient (CF-PI) groups based on pancreatic enzyme usage and fecal elastase. A reference group included healthy, non-diabetic subjects. All CF groups showed reduced insulin secretion as measured by insulinogenic index. The CF-PS patients had normal glucose tolerance. There was a direct correlation between BMI z-score and insulin area under the curve. Patients with CF have reduced insulin secretion during an OGTT regardless of exocrine pancreatic status. The abnormal insulin secretion in all CF patients may predispose them for glucose intolerance, particularly when challenged by inflammation, infection, or nutritional deficiency. In addition, the diminished insulin secretion may contribute to increased catabolism. Lastly, the CF-related diabetes (CFRD) screening guidelines should be followed by all CF patients regardless of pancreatic status. Copyright © 2015 European Cystic Fibrosis Society. Published by Elsevier B.V. All rights reserved.

  1. Insulin Secretion Abnormalities in Exocrine Pancreatic Sufficient Cystic Fibrosis Patients

    PubMed Central

    Wooldridge, Jamie L.; Szczesniak, Rhonda D.; Fenchel, Matthew C.; Elder, Deborah A.

    2015-01-01

    BACKGROUND To assess insulin secretion in pediatric cystic fibrosis (CF) patients with exocrine pancreatic sufficiency. METHODS Glucose and insulin responses during an oral glucose tolerance test (OGTT) were measured in 146 CF patients. Patients were divided into exocrine sufficient (CF-PS) and insufficient (CF-PI) groups based on pancreatic enzyme usage and fecal elastase. A reference group included healthy, non-diabetic subjects. RESULTS All CF groups showed reduced insulin secretion as measured by insulinogenic index. The CF-PS patients had normal glucose tolerance. There was direct correlation between BMI z-score and insulin area under the curve. CONCLUSION Patients with CF have reduced insulin secretion during an OGTT regardless of exocrine pancreatic status. The abnormal insulin secretion in all CF patients may predispose them for glucose intolerance, particularly when challenged by inflammation, infection, or nutritional deficiency. In addition, the diminished insulin secretion may contribute to increased catabolism. Lastly, the CF-related diabetes (CFRD) screening guidelines should be followed by all CF patients regardless of pancreatic status. PMID:25754095

  2. Cell death and impairment of glucose-stimulated insulin secretion induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the {beta}-cell line INS-1E

    SciTech Connect

    Piaggi, Simona; Novelli, Michela; Martino, Luisa; Masini, Matilde; Raggi, Chiara; Orciuolo, Enrico; Masiello, Pellegrino; Casini, Alessandro; De Tata, Vincenzo . E-mail: v.detata@ipg.med.unipi.it

    2007-05-01

    The aim of this research was to characterize 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity on the insulin-secreting {beta}-cell line INS-1E. A sharp decline of cell survival (below 20%) was observed after 1 h exposure to TCDD concentrations between 12.5 and 25 nM. Ultrastructurally, {beta}-cell death was characterized by extensive degranulation, appearance of autophagic vacuoles, and peripheral nuclear condensation. Cytotoxic concentrations of TCDD rapidly induced a dose-dependent increase in intracellular calcium concentration. Blocking calcium entry by EGTA significantly decreased TCDD cytotoxicity. TCDD was also able to rapidly induce mitochondrial depolarization. Interestingly, 1 h exposition of INS-1E cells to very low TCDD concentrations (0.05-1 nM) dramatically impaired glucose-stimulated but not KCl-stimulated insulin secretion. In conclusion, our results clearly show that TCDD exerts a direct {beta}-cell cytotoxic effect at concentrations of 15-25 nM, but also markedly impairs glucose-stimulated insulin secretion at concentrations 20 times lower than these. On the basis of this latter observation we suggest that pancreatic {beta}-cells could be considered a specific and sensitive target for dioxin toxicity.

  3. Sirt1 Regulates Insulin Secretion by Repressing UCP2 in Pancreatic β Cells

    PubMed Central

    Bordone, Laura; Jhala, Ulupi S; Apfeld, Javier; McDonagh, Thomas; Lemieux, Madeleine; McBurney, Michael; Szilvasi, Akos; Easlon, Erin J; Lin, Su-Ju; Guarente, Leonard

    2006-01-01

    Sir2 and insulin/IGF-1 are the major pathways that impinge upon aging in lower organisms. In Caenorhabditis elegans a possible genetic link between Sir2 and the insulin/IGF-1 pathway has been reported. Here we investigate such a link in mammals. We show that Sirt1 positively regulates insulin secretion in pancreatic β cells. Sirt1 represses the uncoupling protein (UCP) gene UCP2 by binding directly to the UCP2 promoter. In β cell lines in which Sirt1 is reduced by SiRNA, UCP2 levels are elevated and insulin secretion is blunted. The up-regulation of UCP2 is associated with a failure of cells to increase ATP levels after glucose stimulation. Knockdown of UCP2 restores the ability to secrete insulin in cells with reduced Sirt1, showing that UCP2 causes the defect in glucose-stimulated insulin secretion. Food deprivation induces UCP2 in mouse pancreas, which may occur via a reduction in NAD (a derivative of niacin) levels in the pancreas and down-regulation of Sirt1. Sirt1 knockout mice display constitutively high UCP2 expression. Our findings show that Sirt1 regulates UCP2 in β cells to affect insulin secretion. PMID:16366736

  4. Constitutively active heat shock factor 1 enhances glucose-driven insulin secretion.

    PubMed

    Uchiyama, Tsuyoshi; Tomono, Shoichi; Utsugi, Toshihiro; Ohyama, Yoshio; Nakamura, Tetsuya; Tomura, Hideaki; Kawazu, Shoji; Okajima, Fumikazu; Kurabayashi, Masahiko

    2011-06-01

    Weak pancreatic β-cell function is a cause of type 2 diabetes mellitus. Glucokinase regulates insulin secretion via phosphorylation of glucose. The present study focused on a system for the self-protection of pancreatic cell by expressing heat shock factor (HSF) and heat shock protein (HSP) to improve insulin secretion without inducing hypoglycemia. We previously generated a constitutively active form of human HSF1 (CA-hHSF1). An adenovirus expressing CA-hHSF1 using the cytomegalovirus promoter was generated to infect mouse insulinoma cells (MIN6 cells). An adenovirus expressing CA-hHSF1 using a human insulin promoter (Ins-CA-hHSF1) was also generated to infect rats. We investigated whether CA-hHSF1 induces insulin secretion in MIN6 cells and whether Ins-CA-hHSF1 can improve blood glucose and serum insulin levels in healthy Wister rats and type 2 diabetes mellitus model rats. CA-hHSF1 expression increased insulin secretion 1.27-fold compared with the overexpression of wild-type hHSF1 in MIN6 cells via induction of HSP90 expression and subsequent activation of glucokinase. This mechanism is associated with activation of both glucokinase and neuronal nitric oxide synthase. Ins-CA-hHSF1 improved blood glucose levels in neonatal streptozotocin-induced diabetic rats. Furthermore, Ins-CA-hHSF1 reduced oral glucose tolerance testing results in healthy Wister rats because of an insulin spike at 15 minutes; however, it did not induce hypoglycemia. CA-hHSF1 induced insulin secretion both in vitro and in vivo. These findings suggest that gene therapy with Ins-CA-hHSF1 will be able to be used to treat patients with type 2 diabetes mellitus and impaired glucose tolerance without causing hypoglycemia at fasting. Copyright © 2011 Elsevier Inc. All rights reserved.

  5. Indian culinary plants enhance glucose-induced insulin secretion and glucose consumption in INS-1 β-cells and 3T3-L1 adipocytes.

    PubMed

    Kaur, Lovedeep; Han, Kyoung-Sik; Bains, Kiran; Singh, Harjinder

    2011-12-01

    Six Indian plants, commonly used as culinary plants, herbs or spices (kikar; jamun; neem; harad; fenugreek; bitter gourd), were screened and compared for their antidiabetic potential in vitro. Aqueous plant extracts were prepared and assessed for their effect on the insulin secretion activity of rat pancreatic INS-1 β-cells and glucose consumption in mouse 3T3-L1 adipocytes in order to study their specific mechanisms of action. The effect of the plant extract concentration (25-1000μg/ml) on insulin release and glucose consumption was also studied. All the extracts had a significant stimulatory effect on the insulin secretion of INS-1 cells. In the presence of kikar extract (100μg/ml), an increase of 228% in insulin release was recorded compared to the control (5.6mM glucose) whereas that was 270% and 367% in the presence of kikar and jamun extracts (500μg/ml), respectively. 3T3-L1 cells treated with jamun extract (100μg/ml) exhibited the highest increase in glucose consumption by the cells (94%, compared with the control) followed by harad (53%) and fenugreek (50%) extracts. A significant inhibitory effect of the fenugreek, kikar and jamun extracts on glucose diffusion across a dialysis membrane suggested that these extracts could partly act by decreasing glucose absorption in the small intestine. The results showed that a combination of these plants in diet could help in the management of both type 1 and type 2 diabetes. Copyright © 2011 Elsevier Ltd. All rights reserved.

  6. Glucagon-like peptide-1 induced signaling and insulin secretion do not drive fuel and energy metabolism in primary rodent pancreatic beta-cells.

    PubMed

    Peyot, Marie-Line; Gray, Joshua P; Lamontagne, Julien; Smith, Peter J S; Holz, George G; Madiraju, S R Murthy; Prentki, Marc; Heart, Emma

    2009-07-13

    Glucagon like peptide-1 (GLP-1) and its analogue exendin-4 (Ex-4) enhance glucose stimulated insulin secretion (GSIS) and activate various signaling pathways in pancreatic beta-cells, in particular cAMP, Ca(2+) and protein kinase-B (PKB/Akt). In many cells these signals activate intermediary metabolism. However, it is not clear whether the acute amplification of GSIS by GLP-1 involves in part metabolic alterations and the production of metabolic coupling factors. GLP-1 or Ex-4 at high glucose caused release (approximately 20%) of the total rat islet insulin content over 1 h. While both GLP-1 and Ex-4 markedly potentiated GSIS in isolated rat and mouse islets, neither had an effect on beta-cell fuel and energy metabolism over a 5 min to 3 h time period. GLP-1 activated PKB without changing glucose usage and oxidation, fatty acid oxidation, lipolysis or esterification into various lipids in rat islets. Ex-4 caused a rise in [Ca(2+)](i) and cAMP but did not enhance energy utilization, as neither oxygen consumption nor mitochondrial ATP levels were altered. The results indicate that GLP-1 barely affects beta-cell intermediary metabolism and that metabolic signaling does not significantly contribute to GLP-1 potentiation of GSIS. The data also indicate that insulin secretion is a minor energy consuming process in the beta-cell, and that the beta-cell is different from most cell types in that its metabolic activation appears to be primarily governed by a "push" (fuel substrate driven) process, rather than a "pull" mechanism secondary to enhanced insulin release as well as to Ca(2+), cAMP and PKB signaling.

  7. LPS-Enhanced Glucose-Stimulated Insulin Secretion Is Normalized by Resveratrol

    PubMed Central

    Nøhr, Mark K.; Dudele, Anete; Poulsen, Morten M.; Ebbesen, Lene H.; Radko, Yulia; Christensen, Lars P.; Jessen, Niels; Richelsen, Bjørn; Lund, Sten; Pedersen, Steen B.

    2016-01-01

    Low-grade inflammation is seen with obesity and is suggested to be a mediator of insulin resistance. The eliciting factor of low-grade inflammation is unknown but increased permeability of gut bacteria-derived lipopolysaccharides (LPS) resulting in endotoxemia could be a candidate. Here we test the effect of LPS and the anti-inflammatory compound resveratrol on glucose homeostasis, insulin levels and inflammation. Mice were subcutaneously implanted with osmotic mini pumps infusing either low-dose LPS or saline for 28 days. Half of the mice were treated with resveratrol delivered through the diet. LPS caused increased inflammation of the liver and adipose tissue (epididymal and subcutaneous) together with enlarged spleens and increased number of leukocytes in the blood. Resveratrol specifically reduced the inflammatory status in epididymal fat (reduced expression of TNFa and Il1b, whereas the increased macrophage infiltration was unaltered) without affecting the other tissues investigated. By LC-MS, we were able to quantitate resveratrol metabolites in epididymal but not subcutaneous adipose tissue. LPS induced insulin resistance as the glucose-stimulated insulin secretion during an oral glucose tolerance test was increased despite similar plasma glucose level resulting in an increase in the insulinogenic index (IGI; delta0-15insulin / delta0-15glucose) from 13.73 to 22.40 pmol/mmol (P < 0.001). This aberration in insulin and glucose homeostasis was normalized by resveratrol. In conclusion: Low-dose LPS enhanced the glucose-stimulated insulin secretion without affecting the blood glucose suggesting increased insulin resistance. Resveratrol restored LPS-induced alteration of the insulin secretion and demonstrated anti-inflammatory effects specifically in epididymal adipose tissue possibly due to preferential accumulation of resveratrol metabolites pointing towards a possible important involvement of this tissue for the effects on insulin resistance and insulin

  8. Size-controlled insulin-secreting cell clusters.

    PubMed

    Mendelsohn, Adam D; Nyitray, Crystal; Sena, Mark; Desai, Tejal A

    2012-12-01

    The search for an effective cure for type I diabetes from the transplantation of encapsulated pancreatic β-cell clusters has so far produced sub-optimal clinical outcomes. Previous efforts have not controlled the size of transplanted clusters, a parameter implicated in affecting long-term viability and the secretion of therapeutically sufficient insulin. Here we demonstrate a method based on covalent attachment of patterned laminin for fabricating uniformly size-controlled insulin-secreting cell clusters. We show that cluster size within the range 40-120μm in diameter affects a variety of therapeutically relevant cellular responses including insulin expression, content and secretion. Our studies elucidate two size-dependent phenomena: (1) as the cluster size increases from 40μm to 60μm, glucose stimulation results in a greater amount of insulin produced per cell; and (2) as the cluster size increases beyond 60μm, sustained glucose stimulation results in a greater amount of insulin secreted per cell. Our study describes a method for producing uniformly sized insulin-secreting cell clusters, and since larger cluster sizes risk nutrient availability limitations, our data suggest that 100-120μm clusters may provide optimal viability and efficacy for encapsulated β-cell transplants as a treatment for type I diabetes and that further in vivo evaluation is warranted.

  9. Pulsatile insulin secretion, impaired glucose tolerance and type 2 diabetes

    PubMed Central

    Satin, Leslie S.; Butler, Peter C.; Ha, Joon; Sherman, Arthur S.

    2015-01-01

    Type 2 diabetes (T2DM) results when increases in beta cell function and/or mass cannot compensate for rising insulin resistance. Numerous studies have documented the longitudinal changes in metabolism that occur during the development of glucose intolerance and lead to T2DM. However, the role of changes in insulin secretion, both amount and temporal pattern has been understudied. Most of the insulin secreted from pancreatic beta cells of the pancreas is released in a pulsatile pattern, which is disrupted in T2DM. Here we review the evidence that changes in beta cell pulsatility occur during the progression from glucose intolerance to T2DM in humans, and contribute significantly to the etiology of the disease. We review the evidence that insulin pulsatility improves the efficacy of secreted insulin on its targets, particularly hepatic glucose production, but also examine evidence that pulsatility alters or is altered by changes in peripheral glucose uptake. Finally, we summarize our current understanding of the biophysical mechanisms responsible for oscillatory insulin secretion. Understanding how insulin pulsatility contributes to normal glucose homeostasis and is altered in metabolic disease states may help improve the treatment of T2DM. PMID:25637831

  10. Deletion of CDKAL1 Affects High-Fat Diet–Induced Fat Accumulation and Glucose-Stimulated Insulin Secretion in Mice, Indicating Relevance to Diabetes

    PubMed Central

    Takeuchi, Fumihiko; Isono, Masato; Akiyama, Koichi; Shimizu, Yukiko; Goto, Motohito; Liang, Yi-Qiang; Yamamoto, Ken; Katsuya, Tomohiro; Fujioka, Akihiro; Ohnaka, Keizo; Takayanagi, Ryoichi; Ogihara, Toshio; Yamori, Yukio; Kato, Norihiro

    2012-01-01

    Background/Objective The CDKAL1 gene is among the best-replicated susceptibility loci for type 2 diabetes, originally identified by genome-wide association studies in humans. To clarify a physiological importance of CDKAL1, we examined effects of a global Cdkal1-null mutation in mice and also evaluated the influence of a CDKAL1 risk allele on body mass index (BMI) in Japanese subjects. Methods In Cdkal1-deficient (Cdkal1−/−) mice, we performed oral glucose tolerance test, insulin tolerance test, and perfusion experiments with and without high-fat feeding. Based on the findings in mice, we tested genetic association of CDKAL1 variants with BMI, as a measure of adiposity, and type 2 diabetes in Japanese. Principal Findings On a standard diet, Cdkal1−/− mice were modestly lighter in weight than wild-type littermates without major alterations in glucose metabolism. On a high fat diet, Cdkal1−/− mice showed significant reduction in fat accumulation (17% reduction in %intraabdominal fat, P = 0.023 vs. wild-type littermates) with less impaired insulin sensitivity at an early stage. High fat feeding did not potentiate insulin secretion in Cdkal1−/− mice (1.0-fold), contrary to the results in wild-type littermates (1.6-fold, P<0.01). Inversely, at a later stage, Cdkal1−/− mice showed more prominent impairment of insulin sensitivity and glucose tolerance. mRNA expression analysis indicated that Scd1 might function as a critical mediator of the altered metabolism in Cdkal1−/− mice. In accordance with the findings in mice, a nominally significant (P<0.05) association between CDKAL1 rs4712523 and BMI was replicated in 2 Japanese general populations comprising 5,695 and 12,569 samples; the risk allele for type 2 diabetes was also associated with decreased BMI. Conclusions Cdkal1 gene deletion is accompanied by modestly impaired insulin secretion and longitudinal fluctuations in insulin sensitivity during high-fat feeding in mice. CDKAL1 may affect

  11. Deletion of CDKAL1 affects high-fat diet-induced fat accumulation and glucose-stimulated insulin secretion in mice, indicating relevance to diabetes.

    PubMed

    Okamura, Tadashi; Yanobu-Takanashi, Rieko; Takeuchi, Fumihiko; Isono, Masato; Akiyama, Koichi; Shimizu, Yukiko; Goto, Motohito; Liang, Yi-Qiang; Yamamoto, Ken; Katsuya, Tomohiro; Fujioka, Akihiro; Ohnaka, Keizo; Takayanagi, Ryoichi; Ogihara, Toshio; Yamori, Yukio; Kato, Norihiro

    2012-01-01

    The CDKAL1 gene is among the best-replicated susceptibility loci for type 2 diabetes, originally identified by genome-wide association studies in humans. To clarify a physiological importance of CDKAL1, we examined effects of a global Cdkal1-null mutation in mice and also evaluated the influence of a CDKAL1 risk allele on body mass index (BMI) in Japanese subjects. In Cdkal1-deficient (Cdkal1⁻/⁻) mice, we performed oral glucose tolerance test, insulin tolerance test, and perfusion experiments with and without high-fat feeding. Based on the findings in mice, we tested genetic association of CDKAL1 variants with BMI, as a measure of adiposity, and type 2 diabetes in Japanese. On a standard diet, Cdkal1⁻/⁻ mice were modestly lighter in weight than wild-type littermates without major alterations in glucose metabolism. On a high fat diet, Cdkal1⁻/⁻ mice showed significant reduction in fat accumulation (17% reduction in %intraabdominal fat, P = 0.023 vs. wild-type littermates) with less impaired insulin sensitivity at an early stage. High fat feeding did not potentiate insulin secretion in Cdkal1⁻/⁻ mice (1.0-fold), contrary to the results in wild-type littermates (1.6-fold, P<0.01). Inversely, at a later stage, Cdkal1⁻/⁻ mice showed more prominent impairment of insulin sensitivity and glucose tolerance. mRNA expression analysis indicated that Scd1 might function as a critical mediator of the altered metabolism in Cdkal1⁻/⁻ mice. In accordance with the findings in mice, a nominally significant (P<0.05) association between CDKAL1 rs4712523 and BMI was replicated in 2 Japanese general populations comprising 5,695 and 12,569 samples; the risk allele for type 2 diabetes was also associated with decreased BMI. Cdkal1 gene deletion is accompanied by modestly impaired insulin secretion and longitudinal fluctuations in insulin sensitivity during high-fat feeding in mice. CDKAL1 may affect such compensatory mechanisms regulating glucose homeostasis

  12. Inhibition of insulin release by synthetic peptides shows that the H3 region at the C-terminal domain of syntaxin-1 is crucial for Ca(2+)- but not for guanosine 5'-[gamma-thio]triphosphate-induced secretion.

    PubMed Central

    Martin, F; Salinas, E; Vazquez, J; Soria, B; Reig, J A

    1996-01-01

    Recently, we have described the presence and possible role of syntaxin in pancreatic beta-cells by using monoclonal antibodies [F. Martin, F. Moya, L. M. Gutierrez, J.A. Reig, B. Soria (1995) Diabetologia 38, 860-863]. In order to characterize further the importance of specific domains of this protein, the functional role of a particular region of the syntaxin-1 molecule has now been investigated by using two synthetic peptides, SynA and SynB, corresponding to two portions of the H3 region at the C-terminal domain of the protein, residues 229-251 and 197-219 respectively. Functional experiments carried out in permeabilized pancreatic beta-cells demonstrate that these peptides inhibit Ca(2+)-dependent insulin release in a dose-dependent manner. This effect is specific because peptides of the same composition but random sequence do not show the same effect. In contrast with this inhibitory effect on Ca(2+)-induced secretion, both peptides increase basal release. However, under the same conditions, SynA and SynB do not affect guanosine 5'-[gamma-thio]triphosphate-induced insulin release. These results demonstrate that specific portions of the H3 region of syntaxin-1 are involved in critical protein-protein interactions specifically during Ca(2+)-induced insulin secretion. PMID:8947488

  13. Bombesin stimulates insulin secretion by a pancreatic islet cell line.

    PubMed Central

    Swope, S L; Schonbrunn, A

    1984-01-01

    The amphibian tetradecapeptide, bombesin (BBS) has been shown to stimulate insulin secretion both in vivo and by pancreatic islet cells in vitro. To determine whether BBS can act directly on pancreatic beta cells, we examined its effects on insulin secretion by HIT-T15 cells (HIT cells), a clonal islet cell line. Addition of 100 nM BBS to HIT cells stimulated insulin release 25-fold within 30 sec. The rapid stimulatory effect of BBS on insulin release was short-lived: the secretory rate returned to basal levels after 90 min of BBS treatment. The decrease in the rate of insulin release in the continued presence of BBS was due not to depletion of intracellular insulin stores but to specific desensitization to this peptide. Stimulation of insulin secretion by BBS was dose dependent with an ED50 value (0.51 +/- 0.15 nM) similar to the concentration of BBS-like immunoreactive material in rat plasma. Five BBS analogs, including porcine gastrin-releasing peptide, were as powerful as BBS in stimulating insulin release. The relative potencies of the analogs tested indicated that the COOH-terminal octapeptide sequence in BBS was sufficient for stimulation of release. In contrast, 14 peptides structurally unrelated to BBS did not alter insulin secretion. BBS action was synergistic with that of glucagon; insulin secretion in the presence of maximal concentrations of both peptides was greater than the additive effects of the two peptides added individually. Somatostatin inhibited BBS-stimulated release by 69 +/- 1% with an ID50 value of 3.2 +/- 0.3 nM. These results show that BBS stimulation of insulin secretion by a clonal pancreatic cell line closely parallels its effects in vivo and support the hypothesis that BBS stimulates insulin secretion by a direct effect on the pancreatic beta cell. The clonal HIT cell line provides a homogeneous cell preparation amenable for studies on the biochemical mechanisms of BBS action in the endocrine pancreas. PMID:6143320

  14. Glucose- and GTP-dependent stimulation of the carboxyl methylation of CDC42 in rodent and human pancreatic islets and pure beta cells. Evidence for an essential role of GTP-binding proteins in nutrient-induced insulin secretion.

    PubMed Central

    Kowluru, A; Seavey, S E; Li, G; Sorenson, R L; Weinhaus, A J; Nesher, R; Rabaglia, M E; Vadakekalam, J; Metz, S A

    1996-01-01

    Several GTP-binding proteins (G-proteins) undergo post-translational modifications (isoprenylation and carboxyl methylation) in pancreatic beta cells. Herein, two of these were identified as CDC42 and rap 1, using Western blotting and immunoprecipitation. Confocal microscopic data indicated that CDC42 is localized only in islet endocrine cells but not in acinar cells of the pancreas. CDC42 undergoes a guanine nucleotide-specific membrane association and carboxyl methylation in normal rat islets, human islets, and pure beta (HIT or INS-1) cells. GTPgammaS-dependent carboxyl methylation of a 23-kD protein was also demonstrable in secretory granule fractions from normal islets or beta cells. AFC (a specific inhibitor of prenyl-cysteine carboxyl methyl transferases) blocked the carboxyl methylation of CDC42 in five types of insulin-secreting cells, without blocking GTPgammaS-induced translocation, implying that methylation is a consequence (not a cause) of transfer to membrane sites. High glucose (but not a depolarizing concentration of K+) induced the carboxyl methylation of CDC42 in intact cells, as assessed after specific immunoprecipitation. This effect was abrogated by GTP depletion using mycophenolic acid and was restored upon GTP repletion by coprovision of guanosine. In contrast, although rap 1 was also carboxyl methylated, it was not translocated to the particulate fraction by GTPgammaS; furthermore, its methylation was also stimulated by 40 mM K+ (suggesting a role which is not specific to nutrient stimulation). AFC also impeded nutrient-induced (but not K+-induced) insulin secretion from islets and beta cells under static or perifusion conditions, whereas an inactive structural analogue of AFC failed to inhibit insulin release. These effects were reproduced not only by S-adenosylhomocysteine (another methylation inhibitor), but also by GTP depletion. Thus, the glucose- and GTP-dependent carboxyl methylation of G-proteins such as CDC42 is an obligate step in

  15. Incretin action maintains insulin secretion, but not hepatic insulin action, in people with impaired fasting glucose.

    PubMed

    Perreault, Leigh; Man, Chiara Dalla; Hunerdosse, Devon M; Cobelli, Claudio; Bergman, Bryan C

    2010-10-01

    To determine whether altered GLP-1 activity contributes to the abnormal endogenous glucose production (EGP) and insulin secretion characteristic of people with impaired fasting glucose (IFG). People with IFG (n=10) and normal glucose tolerance (NGT; n=13) underwent assessment of EGP (via [6,6-(2)H(2)]-glucose infusion). Parameters of whole body insulin action and secretion were estimated by IVGTT and OGTT. Measures of EGP and insulin secretion were made before and after sitagliptin administration. EGP was not different at baseline (glucose R(a); 1.47+/-0.08 vs. 1.46+/-0.05mg/kg/min, IFG vs. NGT, p=0.93). However, when differences in circulating insulin were accounted for (EGPXSSPI; 20.2+/-2.1 vs. 14.4+/-1.0AU, vs. NGT, p=0.03) the hepatic insulin resistance index was significantly higher in IFG. Baseline insulin action (S(i); 2.3+/-0.1x10(-4)/microU/ml vs. 3.5+/-0.4x10(-4)/microU/ml, p=0.01, IFG vs. NGT) and secretion (DI; 587+/-81x10(-4)/min vs. 1171+/-226x10(-4)/min, p=0.04, IFG vs. NGT) were impaired in IFG when evaluated by the IVGTT, but not by OGTT (insulin sensitivity 4.52+/-1.08x10(-4)dl/kg/min vs. 6.73+/-1.16x10(-4)dl/kg/min, IFG vs. NGT, p=0.16; indices of basal (Phi(b)), static (Phi(s)), dynamic (Phi(d)), and total (Phi(t)) insulin secretion, p>0.07). Sitagliptin did not change EGP or insulin secretion in either group. Incretin action maintained insulin secretion, but not hepatic insulin action, in people with IFG.

  16. Nitric Oxide Overproduction Reduces Insulin Secretion from Isolated Islets in Fetal Hypothyroid Rats.

    PubMed

    Rouintan, Z; Farrokhfall, K; Karbalaei, N; Ghasemi, A

    2016-02-01

    Thyroid hormones have developmental effects during fetal life. Fetal hypothyroidism leads to glucose intolerance and reduced insulin secretion capacity. Activity of nitric oxide synthases follows a heterogeneous pattern in hypothyroidism. Overactivity of constitutive nitric oxide synthase (NOS), inhibits glucose-stimulated insulin release. The aim of this study was to examine if reduction in insulin secretion in fetal hypothyroidism is due to overproduction of nitric oxide. Pregnant Wistar rats were divided into 2 groups; the experimental group consumed water containing 0.02% of 6-propyl-2-thiouracil till delivery, while the control group consumed tap water. After delivery serum thyroid hormones were measured. Intravenous glucose tolerance test was performed in 6-month old offspring (n=8). After 3 weeks recovery, pancreatic islets were isolated and insulin secretion, inducible and constitutive nitric oxide synthase activity were measured (n=4). Compared to controls, during intravenous glucose tolerance test, fetal hypothyroid rats had high plasma glucose concentration (p=0.003) and low plasma insulin levels (p=0.012) at 5-20 min and their insulin secretion from isolated islets at basal glucose concentration and in the presence of l-arginine was lower. The nitric oxide synthase inhibitor, NG-nitro-l-arginine methyl ester significantly improved insulin secretion in fetal hypothyroid rats at basal glucose concentration and in the presence of l-arginine. The results showed higher NOS activities in fetal hypothyroid rats (constitutive 17.60±1.09 vs. 47.34±4.44 and inducible 4.09±0.96 vs. 19.97±1.14 pmol/min/mg proteins, p=0.002). In conclusion, NO overproduction through NOS participates in decreased insulin secretion in fetal hypothyroid rats.

  17. mTOR Inhibition: Reduced Insulin Secretion and Sensitivity in a Rat Model of Metabolic Syndrome

    PubMed Central

    Rovira, Jordi; Ramírez-Bajo, María Jose; Banon-Maneus, Elisenda; Moya-Rull, Daniel; Ventura-Aguiar, Pedro; Hierro-Garcia, Natalia; Lazo-Rodriguez, Marta; Revuelta, Ignacio; Torres, Armando; Oppenheimer, Federico; Campistol, Josep M.; Diekmann, Fritz

    2016-01-01

    Background Sirolimus (SRL) has been associated with new-onset diabetes mellitus after transplantation. The aim was to determine the effect of SRL on development of insulin resistance and β-cell toxicity. Methods Lean Zucker rat (LZR) and obese Zucker rat (OZR) were distributed into groups: vehicle and SRL (0.25, 0.5, or 1.0 mg/kg) during 12 or 28 days. Intraperitoneal glucose tolerance test (IPGTT) was evaluated at days 0, 12, 28, and 45. Islet morphometry, β-cell proliferation, and apoptosis were analyzed at 12 days. Islets were isolated to analyze insulin content, insulin secretion, and gene expression. Results After 12 days, SRL treatment only impaired IPGTT in a dose-dependent manner in OZR. Treatment prolongation induced increase of area under the curve of IPGTT in LZR and OZR; however, in contrast to OZR, LZR normalized glucose levels after 2 hours. The SRL reduced pancreas weight and islet proliferation in LZR and OZR as well as insulin content. Insulin secretion was only affected in OZR. Islets from OZR + SRL rats presented a downregulation of Neurod1, Pax4, and Ins2 gene. Genes related with insulin secretion remained unchanged or upregulated. Conclusions In conditions that require adaptive β-cell proliferation, SRL might reveal harmful effects by blocking β-cell proliferation, insulin production and secretion. These effects disappeared when removing the therapy. PMID:27500257

  18. Adipose Triglyceride Lipase Is Implicated in Fuel- and Non-fuel-stimulated Insulin Secretion*

    PubMed Central

    Peyot, Marie-Line; Guay, Claudiane; Latour, Martin G.; Lamontagne, Julien; Lussier, Roxane; Pineda, Marco; Ruderman, Neil B.; Haemmerle, Guenter; Zechner, Rudolf; Joly, Érik; Madiraju, S. R. Murthy; Poitout, Vincent; Prentki, Marc

    2009-01-01

    Reduced lipolysis in hormone-sensitive lipase-deficient mice is associated with impaired glucose-stimulated insulin secretion (GSIS), suggesting that endogenous β-cell lipid stores provide signaling molecules for insulin release. Measurements of lipolysis and triglyceride (TG) lipase activity in islets from HSL−/− mice indicated the presence of other TG lipase(s) in the β-cell. Using real time-quantitative PCR, adipose triglyceride lipase (ATGL) was found to be the most abundant TG lipase in rat islets and INS832/13 cells. To assess its role in insulin secretion, ATGL expression was decreased in INS832/13 cells (ATGL-knockdown (KD)) by small hairpin RNA. ATGL-KD increased the esterification of free fatty acid (FFA) into TG. ATGL-KD cells showed decreased glucose- or Gln + Leu-induced insulin release, as well as reduced response to KCl or palmitate at high, but not low, glucose. The KATP-independent/amplification pathway of GSIS was considerably reduced in ATGL-KD cells. ATGL−/− mice were hypoinsulinemic and hypoglycemic and showed decreased plasma TG and FFAs. A hyperglycemic clamp revealed increased insulin sensitivity and decreased GSIS and arginine-induced insulin secretion in ATGL−/− mice. Accordingly, isolated islets from ATGL−/− mice showed reduced insulin secretion in response to glucose, glucose + palmitate, and KCl. Islet TG content and FFA esterification into TG were increased by 2-fold in ATGL−/− islets, but glucose usage and oxidation were unaltered. The results demonstrate the importance of ATGL and intracellular lipid signaling for fuel- and non-fuel-induced insulin secretion. PMID:19389712

  19. Adipose triglyceride lipase is implicated in fuel- and non-fuel-stimulated insulin secretion.

    PubMed

    Peyot, Marie-Line; Guay, Claudiane; Latour, Martin G; Lamontagne, Julien; Lussier, Roxane; Pineda, Marco; Ruderman, Neil B; Haemmerle, Guenter; Zechner, Rudolf; Joly, Erik; Madiraju, S R Murthy; Poitout, Vincent; Prentki, Marc

    2009-06-19

    Reduced lipolysis in hormone-sensitive lipase-deficient mice is associated with impaired glucose-stimulated insulin secretion (GSIS), suggesting that endogenous beta-cell lipid stores provide signaling molecules for insulin release. Measurements of lipolysis and triglyceride (TG) lipase activity in islets from HSL(-/-) mice indicated the presence of other TG lipase(s) in the beta-cell. Using real time-quantitative PCR, adipose triglyceride lipase (ATGL) was found to be the most abundant TG lipase in rat islets and INS832/13 cells. To assess its role in insulin secretion, ATGL expression was decreased in INS832/13 cells (ATGL-knockdown (KD)) by small hairpin RNA. ATGL-KD increased the esterification of free fatty acid (FFA) into TG. ATGL-KD cells showed decreased glucose- or Gln + Leu-induced insulin release, as well as reduced response to KCl or palmitate at high, but not low, glucose. The K(ATP)-independent/amplification pathway of GSIS was considerably reduced in ATGL-KD cells. ATGL(-/-) mice were hypoinsulinemic and hypoglycemic and showed decreased plasma TG and FFAs. A hyperglycemic clamp revealed increased insulin sensitivity and decreased GSIS and arginine-induced insulin secretion in ATGL(-/-) mice. Accordingly, isolated islets from ATGL(-/-) mice showed reduced insulin secretion in response to glucose, glucose + palmitate, and KCl. Islet TG content and FFA esterification into TG were increased by 2-fold in ATGL(-/-) islets, but glucose usage and oxidation were unaltered. The results demonstrate the importance of ATGL and intracellular lipid signaling for fuel- and non-fuel-induced insulin secretion.

  20. Stimulus-secretion coupling of arginine-induced insulin release. Uptake of metabolized and nonmetabolized cationic amino acids by pancreatic islets

    SciTech Connect

    Blachier, F.; Mourtada, A.; Sener, A.; Malaisse, W.J.

    1989-01-01

    In order to assess the possible role of L-arginine accumulation in islet cells as a determinant of its insulinotropic action, the uptake of L-arginine and other cationic amino acids (L-ornithine, L-homoarginine, D,L-alpha-methylornithine, D,L-alpha-difluoromethylornithine) by rat pancreatic islets was compared to the ionic and secretory responses of the islets to the same amino acids. A tight correlation was found between the net uptake of these amino acids and their capacity to stimulate 86Rb efflux, 45Ca uptake and efflux, and insulin release. In the latter respect, there was little difference between metabolized and nonmetabolized amino acids. Thus, although L-homoarginine and 4-amino-1-guanylpiperidine-4-carboxylic acid failed to act as a substrate for either arginase or amino acid aminotransferase in islet homogenates, they both stimulated 86Rb efflux, 45Ca uptake and efflux, and insulin secretion in intact islets. These findings are compatible with the view that the accumulation of these positively charged amino acids in islet cells represents an essential determinant of their secretory action. Hence, the release of insulin evoked by these amino acids could be due to depolarization of the plasma membrane with subsequent gating of voltage-sensitive Ca2+ channels and/or to some other biophysical effect, as suggested by the persistence of a sizeable secretory response to L-arginine or L-ornithine in islets perifused at a high concentrations of extracellular K+ (50 mM).

  1. Green tea polyphenols modulate insulin secretion by inhibiting glutamate dehydrogenase.

    PubMed

    Li, Changhong; Allen, Aron; Kwagh, Jae; Doliba, Nicolai M; Qin, Wei; Najafi, Habiba; Collins, Heather W; Matschinsky, Franz M; Stanley, Charles A; Smith, Thomas J

    2006-04-14

    Insulin secretion by pancreatic beta-cells is stimulated by glucose, amino acids, and other metabolic fuels. Glutamate dehydrogenase (GDH) has been shown to play a regulatory role in this process. The importance of GDH was underscored by features of hyperinsulinemia/hyperammonemia syndrome, where a dominant mutation causes the loss of inhibition by GTP and ATP. Here we report the effects of green tea polyphenols on GDH and insulin secretion. Of the four compounds tested, epigallocatechin gallate (EGCG) and epicatechin gallate were found to inhibit GDH with nanomolar ED(50) values and were therefore found to be as potent as the physiologically important inhibitor GTP. Furthermore, we have demonstrated that EGCG inhibits BCH-stimulated insulin secretion, a process that is mediated by GDH, under conditions where GDH is no longer inhibited by high energy metabolites. EGCG does not affect glucose-stimulated insulin secretion under high energy conditions where GDH is probably fully inhibited. We have further shown that these compounds act in an allosteric manner independent of their antioxidant activity and that the beta-cell stimulatory effects are directly correlated with glutamine oxidation. These results demonstrate that EGCG, much like the activator of GDH (BCH), can facilitate dissecting the complex regulation of insulin secretion by pharmacologically modulating the effects of GDH.

  2. α-Synuclein binds the KATP channel at insulin-secretory granules and inhibits insulin secretion

    PubMed Central

    Geng, Xuehui; Lou, Haiyan; Wang, Jian; Li, Lehong; Swanson, Alexandra L.; Sun, Ming; Beers-Stolz, Donna; Watkins, Simon; Perez, Ruth G.

    2011-01-01

    α-Synuclein has been studied in numerous cell types often associated with secretory processes. In pancreatic β-cells, α-synuclein might therefore play a similar role by interacting with organelles involved in insulin secretion. We tested for α-synuclein localizing to insulin-secretory granules and characterized its role in glucose-stimulated insulin secretion. Immunohistochemistry and fluorescent sulfonylureas were used to test for α-synuclein localization to insulin granules in β-cells, immunoprecipitation with Western blot analysis for interaction between α-synuclein and KATP channels, and ELISA assays for the effect of altering α-synuclein expression up or down on insulin secretion in INS1 cells or mouse islets, respectively. Differences in cellular phenotype between α-synuclein knockout and wild-type β-cells were found by using confocal microscopy to image the fluorescent insulin biosensor Ins-C-emGFP and by using transmission electron microscopy. The results show that anti-α-synuclein antibodies labeled secretory organelles within β-cells. Anti-α-synuclein antibodies colocalized with KATP channel, anti-insulin, and anti-C-peptide antibodies. α-Synuclein coimmunoprecipitated in complexes with KATP channels. Expression of α-synuclein downregulated insulin secretion at 2.8 mM glucose with little effect following 16.7 mM glucose stimulation. α-Synuclein knockout islets upregulated insulin secretion at 2.8 and 8.4 mM but not 16.7 mM glucose, consistent with the depleted insulin granule density at the β-cell surface membranes observed in these islets. These findings demonstrate that α-synuclein interacts with KATP channels and insulin-secretory granules and functionally acts as a brake on secretion that glucose stimulation can override. α-Synuclein might play similar roles in diabetes as it does in other degenerative diseases, including Alzheimer's and Parkinson's diseases. PMID:20858756

  3. Dissecting the relationship between obesity and hyperinsulinemia: Role of insulin secretion and insulin clearance.

    PubMed

    Kim, Mee Kyoung; Reaven, Gerald M; Kim, Sun H

    2017-02-01

    The aim of this study was to better delineate the complex interrelationship among insulin resistance (IR), secretion rate (ISR), and clearance rate (ICR) to increase plasma insulin concentrations in obesity. Healthy volunteers (92 nondiabetic individuals) had an insulin suppression test to measure IR and graded-glucose infusion test to measure ISR and ICR. Obesity was defined as a body mass index (BMI) ≥30 kg/m(2) , and IR was defined as steady-state plasma glucose (SSPG) ≥10 mmol/L during the insulin suppression test. Plasma glucose and insulin concentrations, ISR, and ICR were compared in three groups: insulin sensitive/overweight; insulin sensitive/obesity; and insulin resistant/obesity. Compared with the insulin-sensitive/overweight group, the insulin-sensitive/obesity had significantly higher insulin area under the curve (AUC) and ISR AUC during the graded-glucose infusion test (P < 0.001). Glucose AUC and ICR were similar. The insulin-resistant/obesity group had higher insulin AUC and ISR AUC compared with the insulin-sensitive/obesity but also had higher glucose AUC and decreased ICR (P < 0.01). In multivariate analysis, both BMI and SSPG were significantly associated with ISR. Plasma insulin concentration and ISR are increased in individuals with obesity, irrespective of degree of IR, but a decrease in ICR is confined to the subset of individuals with IR. © 2016 The Obesity Society.

  4. Potentiation of Calcium Influx and Insulin Secretion in Pancreatic Beta Cell by the Specific TREK-1 Blocker Spadin

    PubMed Central

    Hivelin, Céline; Béraud-Dufour, Sophie; Devader, Christelle; Moreno, Sébastien; Moha ou Maati, Hamid; Djillani, Alaeddine; Heurteaux, Catherine; Borsotto, Marc

    2016-01-01

    Inhibition of the potassium channels TREK-1 by spadin (SPA) is currently thought to be a promising therapeutic target for the treatment of depression. Since these channels are expressed in pancreatic β-cells, we investigated their role in the control of insulin secretion and glucose homeostasis. In this study, we confirmed the expression of TREK-1 channels in the insulin secreting MIN6-B1 β-cell line and in mouse islets. We found that their blockade by SPA potentiated insulin secretion induced by potassium chloride dependent membrane depolarization. Inhibition of TREK-1 by SPA induced a decrease of the resting membrane potential (ΔVm ~ 12 mV) and increased the cytosolic calcium concentration. In mice, administration of SPA enhanced the plasma insulin level stimulated by glucose, confirming its secretagogue effect observed in vitro. Taken together, this work identifies SPA as a novel potential pharmacological agent able to control insulin secretion and glucose homeostasis. PMID:28105440

  5. Cooperation between cAMP signalling and sulfonylurea in insulin secretion.

    PubMed

    Shibasaki, T; Takahashi, T; Takahashi, H; Seino, S

    2014-09-01

    Although glucose is physiologically the most important regulator of insulin secretion, glucose-induced insulin secretion is modulated by hormonal and neural inputs to pancreatic β-cells. Most of the hormones and neurotransmitters evoke intracellular signals such as cAMP, Ca²⁺ , and phospholipid-derived molecules by activating G protein-coupled receptors (GPCRs). In particular, cAMP is a key second messenger that amplifies insulin secretion in a glucose concentration-dependent manner. The action of cAMP on insulin secretion is mediated by both protein kinase A (PKA)-dependent and Epac2A-dependent mechanisms. Many of the proteins expressed in β-cells are phosphorylated by PKA in vitro, but only a few proteins in which PKA phosphorylation directly affects insulin secretion have been identified. On the other hand, Epac2A activates the Ras-like small G protein Rap in a cAMP-dependent manner. Epac2A is also directly activated by various sulfonylureas, except for gliclazide. 8-pCPT-2'-O-Me-cAMP, an Epac-selective cAMP analogue, and glibenclamide, a sulfonylurea, synergistically activate Epac2A and Rap1, whereas adrenaline, which suppresses cAMP production in pancreatic β-cells, blocks activation of Epac2A and Rap1 by glibenclamide. Thus, cAMP signalling and sulfonylurea cooperatively activate Epac2A and Rap1. This interaction could account, at least in part, for the synergistic effects of incretin-related drugs and sulfonylureas in insulin secretion. Accordingly, clarification of the mechanism of Epac2A activation may provide therapeutic strategies to improve insulin secretion in diabetes.

  6. Selective Serotonin Reuptake Inhibitors (SSRIs) Inhibit Insulin Secretion and Action in Pancreatic β Cells*

    PubMed Central

    Isaac, Roi; Boura-Halfon, Sigalit; Gurevitch, Diana; Shainskaya, Alla; Levkovitz, Yechiel; Zick, Yehiel

    2013-01-01

    Selective serotonin reuptake inhibitors (SSRIs) are antidepressants used for the treatment of mood and anxiety disorders. Here, we demonstrate that incubation (2 h) of murine islets or Min6 β cell line with the SSRIs paroxetine, fluoxetine, or sertraline inhibited insulin-induced Tyr phosphorylation of insulin receptor substrate (IRS)-2 protein and the activation of its downstream targets Akt and the ribosomal protein S6 kinase-1 (S6K1). Inhibition was dose-dependent with half-maximal effects at ∼15–20 μm. It correlated with a rapid dephosphorylation and activation of the IRS kinase GSK3β. Introduction of GSK3β siRNAs eliminated the inhibitory effects of the SSRIs. Inhibition of IRS-2 action by 30 μm SSRI was associated with a marked inhibition of glucose-stimulated insulin secretion from murine and human pancreatic islets. Secretion induced by basic secretagogues (KCl and Arg) was not affected by these drugs. Prolonged treatment (16 h) of Min6 cells with sertraline resulted in the induction of inducible nitric oxide synthase; activation of endoplasmic reticulum stress, and the initiation of the unfolded protein response, manifested by enhanced transcription of ATF4 and C/EBP homologous protein. This triggered an apoptotic process, manifested by enhanced caspase 3/7 activity, which resulted in β cell death. These findings implicate SSRIs as inhibitors of IRS protein function and insulin action through the activation of GSK3β. They further suggest that SSRIs inhibit insulin secretion; induce the unfolded protein response; activate an apoptotic process, and trigger β cell death. Given that SSRIs promote insulin resistance while inhibiting insulin secretion, these drugs might accelerate the transition from an insulin-resistant state to overt diabetes. PMID:23275337

  7. Circulating retinol-binding protein-4, insulin sensitivity, insulin secretion, and insulin disposition index in obese and nonobese subjects.

    PubMed

    Broch, Montserrat; Vendrell, Joan; Ricart, Wifredo; Richart, Cristóbal; Fernández-Real, José-Manuel

    2007-07-01

    Recent investigations disclosed an upregulation of retinol-binding protein-4 (RBP4) in the adipose tissue of several insulin-resistant mouse models and increased serum RBP4 concentration in subjects with obesity and type 2 diabetes in association with insulin resistance. There is some experimental evidence that RBP4 also could been linked to insulin secretion. We aimed to evaluate insulin secretion, insulin sensitivity, insulin disposition index (minimal model analysis), and circulating RBP4 (enzyme-linked immunosorbent assay) in nondiabetic men with a wide range of obesity (n = 107). Serum RBP4 concentration was nonsignificantly different among lean, overweight, and obese subjects. Circulating RBP4 was not associated with age, BMI, waist-to-hip ratio, or metabolic parameters, including insulin sensitivity (r = -0.03, P = 0.6). On the contrary, circulating RBP4 was negatively associated with insulin secretion, especially in obese subjects (r = -0.48, P = 0.007), in whom RBP4 also was linked to insulin disposition index (r = -0.44, P = 0.01). On multiple regression analyses to predict insulin secretion (acute insulin response [AIR(g)]), insulin sensitivity was the only factor that contributed to 17% of AIR(g) variance in nonobese subjects. In obese subjects, however, RBP4 emerged as an independent factor that contributed independently to AIR(g) variance (23%). Our results suggest that oversecretion of RBP4 may negatively affect beta-cell function directly or by preventing the binding of transthyretin to its receptor. These mechanisms could be behind the association between increased circulating RBP4 and type 2 diabetes. RBP4 could be one signal from insulin-resistant tissues that impacts on beta-cell secretion.

  8. Thrombin stimulates insulin secretion via protease-activated receptor-3.

    PubMed

    Hänzelmann, Sonja; Wang, Jinling; Güney, Emre; Tang, Yunzhao; Zhang, Enming; Axelsson, Annika S; Nenonen, Hannah; Salehi, Albert S; Wollheim, Claes B; Zetterberg, Eva; Berntorp, Erik; Costa, Ivan G; Castelo, Robert; Rosengren, Anders H

    2015-01-01

    The disease mechanisms underlying type 2 diabetes (T2D) remain poorly defined. Here we aimed to explore the pathophysiology of T2D by analyzing gene co-expression networks in human islets. Using partial correlation networks we identified a group of co-expressed genes ('module') including F2RL2 that was associated with glycated hemoglobin. F2Rl2 is a G-protein-coupled receptor (GPCR) that encodes protease-activated receptor-3 (PAR3). PAR3 is cleaved by thrombin, which exposes a 6-amino acid sequence that acts as a 'tethered ligand' to regulate cellular signaling. We have characterized the effect of PAR3 activation on insulin secretion by static insulin secretion measurements, capacitance measurements, studies of diabetic animal models and patient samples. We demonstrate that thrombin stimulates insulin secretion, an effect that was prevented by an antibody that blocks the thrombin cleavage site of PAR3. Treatment with a peptide corresponding to the PAR3 tethered ligand stimulated islet insulin secretion and single β-cell exocytosis by a mechanism that involves activation of phospholipase C and Ca(2+) release from intracellular stores. Moreover, we observed that the expression of tissue factor, which regulates thrombin generation, was increased in human islets from T2D donors and associated with enhanced β-cell exocytosis. Finally, we demonstrate that thrombin generation potential in patients with T2D was associated with increased fasting insulin and insulinogenic index. The findings provide a previously unrecognized link between hypercoagulability and hyperinsulinemia and suggest that reducing thrombin activity or blocking PAR3 cleavage could potentially counteract the exaggerated insulin secretion that drives insulin resistance and β-cell exhaustion in T2D.

  9. Minireview: Dopaminergic Regulation of Insulin Secretion from the Pancreatic Islet

    PubMed Central

    Ustione, Alessandro

    2013-01-01

    Exogenous dopamine inhibits insulin secretion from pancreatic β-cells, but the lack of dopaminergic neurons in pancreatic islets has led to controversy regarding the importance of this effect. Recent data, however, suggest a plausible physiologic role for dopamine in the regulation of insulin secretion. We review the literature underlying our current understanding of dopaminergic signaling that can down-regulate glucose-stimulated insulin secretion from pancreatic islets. In this negative feedback loop, dopamine is synthesized in the β-cells from circulating l-dopa, serves as an autocrine signal that is cosecreted with insulin, and causes a tonic inhibition on glucose-stimulated insulin secretion. On the whole animal scale, l-dopa is produced by cells in the gastrointestinal tract, and its concentration in the blood plasma increases following a mixed meal. By reviewing the outcome of certain types of bariatric surgery that result in rapid amelioration of glucose tolerance, we hypothesize that dopamine serves as an “antiincretin” signal that counterbalances the stimulatory effect of glucagon-like peptide 1. PMID:23744894

  10. Prenatal Programming of Insulin Secretion in Intrauterine Growth Restriction

    PubMed Central

    Gatford, Kathryn L.; Simmons, Rebecca A.

    2014-01-01

    Intrauterine growth restriction (IUGR) impairs insulin secretion in humans and in animal models of IUGR. Several underlying mechanisms have been implicated, including decreased expression of molecular regulators of β-cell mass and function, in some cases shown to be due to epigenetic changes initiated by an adverse fetal environment. Alterations in cell cycle progression contribute to loss of β-cell mass, whereas decreased islet vascularity and mitochondrial dysfunction impair β-cell function in IUGR rodents. Animal models of IUGR sharing similar insulin secretion outcomes as the IUGR human are allowing underlying mechanisms to be identified. This review will focus on models of uteroplacental in sufficiency. PMID:23820120

  11. Prenatal programming of insulin secretion in intrauterine growth restriction.

    PubMed

    Gatford, Kathryn L; Simmons, Rebecca A

    2013-09-01

    Intrauterine growth restriction (IUGR) impairs insulin secretion in humans and in animal models of IUGR. Several underlying mechanisms have been implicated, including decreased expression of molecular regulators of β-cell mass and function, in some cases shown to be due to epigenetic changes initiated by an adverse fetal environment. Alterations in cell cycle progression contribute to loss of β-cell mass, whereas decreased islet vascularity and mitochondrial dysfunction impair β-cell function in IUGR rodents. Animal models of IUGR sharing similar insulin secretion outcomes as the IUGR human are allowing underlying mechanisms to be identified. This review will focus on models of uteroplacental insufficiency.

  12. Cell signalling in insulin secretion: the molecular targets of ATP, cAMP and sulfonylurea.

    PubMed

    Seino, S

    2012-08-01

    Clarification of the molecular mechanisms of insulin secretion is crucial for understanding the pathogenesis and pathophysiology of diabetes and for development of novel therapeutic strategies for the disease. Insulin secretion is regulated by various intracellular signals generated by nutrients and hormonal and neural inputs. In addition, a variety of glucose-lowering drugs including sulfonylureas, glinide-derivatives, and incretin-related drugs such as dipeptidyl peptidase IV (DPP-4) inhibitors and glucagon-like peptide 1 (GLP-1) receptor agonists are used for glycaemic control by targeting beta cell signalling for improved insulin secretion. There has been a remarkable increase in our understanding of the basis of beta cell signalling over the past two decades following the application of molecular biology, gene technology, electrophysiology and bioimaging to beta cell research. This review discusses cell signalling in insulin secretion, focusing on the molecular targets of ATP, cAMP and sulfonylurea, an essential metabolic signal in glucose-induced insulin secretion (GIIS), a critical signal in the potentiation of GIIS, and the commonly used glucose-lowering drug, respectively.

  13. Cardiorespiratory fitness predicts insulin action and secretion in healthy individuals.

    PubMed

    Larsen, Filip J; Anderson, Martin; Ekblom, Björn; Nyström, Thomas

    2012-01-01

    Long-term cardiorespiratory fitness (CRF) and the development of type 2 diabetes mellitus are inversely correlated. Here, we examined the relationships between peak oxygen uptake (VO(2)peak), on the one hand, and glucose infusion rate at rest (GIR(rest)) and during exercise (GIR(exercise)), as well as insulin secretion (both the early and late phases of response [area under the curve {AUC}(insulin)]), on the other. Eight male and 4 female healthy, lean, nonsmoking volunteers were recruited. The VO(2)peak was measured during graded exercise on a cycle ergometer until exhaustion was reached. The GIR(rest) and GIR(exercise) were determined using a euglycemic-hyperinsulinemic clamp, and insulin secretion at rest was evaluated with an intravenous glucose tolerance test. The VO(2)peak correlated positively to GIR(rest) (r = 0.81, P = .001) and GIR(exercise) (r = 0.87, P < .001) and negatively to AUC(insulin) (r = -0.64, P = .03). The respiratory exchange ratio (RER) during insulin infusion was positively correlated to GIR(rest) (r = 0.83, P < .001) and GIR(exercise) (r = 0.86, P < .01) and negatively correlated to both the early insulin response (r = -0.86, P < .0001) and AUC(insulin) (r = -0.87, P = .001). The VO(2)peak accounted for 45% of the variability in RER (R(2) = 0.45, P = .035). In this healthy population, CRF and RER were highly correlated to insulin sensitivity and secretion, as well as to the ability to alter the substrate being oxidized during exercise. These findings highlight the importance of good CRF to maintaining normal insulin action.

  14. Decreased irisin secretion contributes to muscle insulin resistance in high-fat diet mice.

    PubMed

    Yang, Zaigang; Chen, Xu; Chen, Yujuan; Zhao, Qian

    2015-01-01

    Recent studies have revealed the relationship between irisin and insulin signaling, while positive associations of muscle FNDC5 with insulin resistance is observed. However, the functional mechanism of irisin on muscle insulin resistance is still obscure. This study aims to investigate the effect of irisin on muscle insulin action. Diabetic mouse model was established by high fat diet (HFD) induced obesity in C57BL/6 mice. Body indexes and serum levels of triglyceride (TG), blood glucose and insulin were record. Oral glucose tolerance test (OGTT) was performed before being killed. Circulating irisin level was also detected, while FNDC5/irisin expression was determined by RT-PCR and western blot analysis in both muscle and adipose tissues. Insulin action was further evaluated by the phosphorylation of AKT and Erk, and palmitic acid treated muscle cells were introduced for mimicking diabetic status in vitro. Obvious obese feathers associated with type 2 diabetes were observed in HFD feeding mice, with decreased circulating irisin level and FNDC5/irisin secretion in adipose tissues. Although FNDC5/irisin expression showed little change in skeletal muscle, the insulin action was inhibited significantly. Moreover, palmitic acid treated muscle cells showed similar inhibition of insulin action, and FNDC5/irisin expression change. Besides, insulin action could be reversed by irisin addition in muscle cells. HFD induced obese mice showed decreased irisin secretion from adipose tissues, which might contribute to muscle insulin resistance. Furthermore, irisin addition could recover insulin action in palmitic acid treated muscle cells, indicating the importance of irisin for preserving insulin signaling.

  15. Insulin Stimulates S100B Secretion and These Proteins Antagonistically Modulate Brain Glucose Metabolism.

    PubMed

    Wartchow, Krista Minéia; Tramontina, Ana Carolina; de Souza, Daniela F; Biasibetti, Regina; Bobermin, Larissa D; Gonçalves, Carlos-Alberto

    2016-06-01

    Brain metabolism is highly dependent on glucose, which is derived from the blood circulation and metabolized by the astrocytes and other neural cells via several pathways. Glucose uptake in the brain does not involve insulin-dependent glucose transporters; however, this hormone affects the glucose influx to the brain. Changes in cerebrospinal fluid levels of S100B (an astrocyte-derived protein) have been associated with alterations in glucose metabolism; however, there is no evidence whether insulin modulates glucose metabolism and S100B secretion. Herein, we investigated the effect of S100B on glucose metabolism, measuring D-(3)H-glucose incorporation in two preparations, C6 glioma cells and acute hippocampal slices, and we also investigated the effect of insulin on S100B secretion. Our results showed that: (a) S100B at physiological levels decreases glucose uptake, through the multiligand receptor RAGE and mitogen-activated protein kinase/ERK signaling, and (b) insulin stimulated S100B secretion via PI3K signaling. Our findings indicate the existence of insulin-S100B modulation of glucose utilization in the brain tissue, and may improve our understanding of glucose metabolism in several conditions such as ketosis, streptozotocin-induced dementia and pharmacological exposure to antipsychotics, situations that lead to changes in insulin signaling and extracellular levels of S100B.

  16. Pre-germinated brown rice prevents high-fat diet induced hyperglycemia through elevated insulin secretion and glucose metabolism pathway in C57BL/6J strain mice

    PubMed Central

    Shen, Kuo-Ping; Hao, Chi-Long; Yen, Hsueh-Wei; Chen, Chun-Yen; Wu, Bin-Nan; Lin, Hui-Li

    2015-01-01

    This study investigated the effect and mechanism of pre-germinated brown rice (PGBR) prevented hyperglycemia in C57BL/6J mice fed high-fat-diet (HFD). Normal six-week-old mice were randomly divided into three groups. Group 1 was fed standard-regular-diet (SRD) and group 2 was fed HFD for 16 weeks. In group 3, the mice were fed a HFD with its carbohydrate replaced with PGBR for 16 weeks. Comparing the SRD and HFD groups, we found the HFD group had higher blood pressure, higher concentrations of blood glucose and HbA1c. The HFD group had less protein expression of insulin receptor (IR), insulin receptor substrate-1 (IRS-1), phosphatidylinositol-3-kinase (PI3K), glucose transporter-4 (GLUT-4) and glucokinase (GCK) and greater expression of glucogen synthase kinase (GSK) in skeletal muscle. The HFD group also had less expression of IR, serine/threonine kinase PI3K-linked protein kinase B (Akt/PKB), AMP-activated protein kinase (AMPK), GCK and peroxisome proliferator-activated receptor γ (PPARγ) in liver. In the HFD + PGBR group, the PGBR could reverse the disorders of blood pressure, blood glucose, HbA1c and increase insulin concentration. PGBR increased the IR, IRS-1, PI3K, Akt, GLUT-1 and GLUT-4 proteins, and ameliorated AMPK, GCK, GSK and PPARγ proteins. Together, PGBR prevented HFD-induced hyperglycemia through improving insulin levels, insulin receptor, glucose transporters and enhancing glucose metabolism. PMID:25834303

  17. Optogenetic control of insulin secretion by pancreatic β-cells in vitro and in vivo.

    PubMed

    Kushibiki, T; Okawa, S; Hirasawa, T; Ishihara, M

    2015-07-01

    The present study assessed the ability of optogenetics techniques to provide a better understanding of the control of insulin secretion, particularly regarding pancreatic β-cell function in homeostasis and pathological conditions such as diabetes mellitus (DM). We used optogenetics to investigate whether insulin secretion and blood glucose homeostasis could be controlled by regulating intracellular calcium ion concentrations ([Ca(2+)]i) in a mouse pancreatic β-cell line (MIN6) transfected with the optogenetic protein channelrhodopsin-2 (ChR2). The ChR2-transfected MIN6 (ChR2-MIN6) cells secreted insulin following irradiation with a laser (470 nm). The increase in [Ca(2+)]i was accompanied by elevated levels of messenger RNAs that encode calcium/calmodulin-dependent protein kinase II delta and adenylate cyclase 1. ChR2-MIN6 cells suspended in matrigel were inoculated into streptozotocin-induced diabetic mice that were then subjected to a glucose tolerance test. Laser irradiation of these mice caused a significant decrease in blood glucose, and the irradiated implanted cells expressed insulin. These findings demonstrate the power of optogenetics to precisely and efficiently controlled insulin secretion by pancreatic β-cells 'on demand', in contrast to techniques using growth factors or chemical inducers. Optogenetic technology shows great promise for understanding the mechanisms of glucose homeostasis and for developing treatments for metabolic diseases such as DM.

  18. Perspective: emerging evidence for signaling roles of mitochondrial anaplerotic products in insulin secretion.

    PubMed

    MacDonald, Michael J; Fahien, Leonard A; Brown, Laura J; Hasan, Noaman M; Buss, Julian D; Kendrick, Mindy A

    2005-01-01

    The importance of mitochondrial biosynthesis in stimulus secretion coupling in the insulin-producing beta-cell probably equals that of ATP production. In glucose-induced insulin secretion, the rate of pyruvate carboxylation is very high and correlates more strongly with the glucose concentration the beta-cell is exposed to (and thus with insulin release) than does pyruvate decarboxylation, which produces acetyl-CoA for metabolism in the citric acid cycle to produce ATP. The carboxylation pathway can increase the levels of citric acid cycle intermediates, and this indicates that anaplerosis, the net synthesis of cycle intermediates, is important for insulin secretion. Increased cycle intermediates will alter mitochondrial processes, and, therefore, the synthesized intermediates must be exported from mitochondria to the cytosol (cataplerosis). This further suggests that these intermediates have roles in signaling insulin secretion. Although evidence is quite good that all physiological fuel secretagogues stimulate insulin secretion via anaplerosis, evidence is just emerging about the possible extramitochondrial roles of exported citric acid cycle intermediates. This article speculates on their potential roles as signaling molecules themselves and as exporters of equivalents of NADPH, acetyl-CoA and malonyl-CoA, as well as alpha-ketoglutarate as a substrate for hydroxylases. We also discuss the "succinate mechanism," which hypothesizes that insulin secretagogues produce both NADPH and mevalonate. Finally, we discuss the role of mitochondria in causing oscillations in beta-cell citrate levels. These parallel oscillations in ATP and NAD(P)H. Oscillations in beta-cell plasma membrane electrical potential, ATP/ADP and NAD(P)/NAD(P)H ratios, and glycolytic flux are known to correlate with pulsatile insulin release. Citrate oscillations might synchronize oscillations of individual mitochondria with one another and mitochondrial oscillations with oscillations in glycolysis

  19. Quetiapine treatment in youth is associated with decreased insulin secretion.

    PubMed

    Ngai, Ying Fai; Sabatini, Paul; Nguyen, Duc; Davidson, Jana; Chanoine, Jean-Pierre; Devlin, Angela M; Lynn, Francis C; Panagiotopoulos, Constadina

    2014-06-01

    Second-generation antipsychotics (SGAs) are commonly prescribed to youth but are associated with metabolic effects including obesity and diabetes. The mechanisms underlying diabetes development are unclear. The purpose of this study was to compare glucose homeostasis, insulin sensitivity, insulin secretion, and overall β-cell function in risperidone-treated, quetiapine-treated, and SGA-naive youth with mental illness. We conducted a cross-sectional study in which youth aged 9 to 18 years underwent a 2-hour oral glucose tolerance test. Indices for insulin sensitivity (Matsuda index), insulin secretion (insulinogenic index), and β-cell function (insulin secretion-sensitivity index-2 [ISSI-2]) were calculated. A total of 18 SGA-naive, 20 risperidone-treated, and 16 quetiapine-treated youth participated. The 3 groups were similar in age, sex, ethnicity, body mass index standardized for age and sex, pubertal status, degree of psychiatric illness, psychiatric diagnoses, and other medications. The median treatment duration was 17 months (range, 3-91 months) for risperidone-treated youth and 10 months (range, 3-44 months) for quetiapine-treated youth. The quetiapine-treated group had lower insulinogenic index (P < 0.01) and lower ISSI-2 (P < 0.01) compared with that in the SGA-naive group. Only the body mass index standardized for age and sex was negatively associated with Matsuda index (β = -0.540, P < 0.001) in all youth. Quetiapine treatment was negatively associated with insulinogenic index (β = -0.426, P = 0.007) and ISSI-2 (β = -0.433, P = 0.008). Quetiapine reduced the insulin expression in isolated mouse islets suggesting a direct β-cell effect. Our results suggest that quetiapine treatment in youth is associated with impaired β-cell function, specifically lower insulin secretion. Prospective longitudinal studies are required to understand the progression of β-cell dysfunction after quetiapine initiation.

  20. Effects of I(Ks) channel inhibitors in insulin-secreting INS-1 cells.

    PubMed

    Ullrich, Susanne; Su, Jiping; Ranta, Felicia; Wittekindt, Oliver H; Ris, Frederic; Rösler, Martin; Gerlach, Uwe; Heitzmann, Dirk; Warth, Richard; Lang, Florian

    2005-12-01

    Potassium channels regulate insulin secretion. The closure of K(ATP) channels leads to membrane depolarisation, which triggers Ca(2+) influx and stimulates insulin secretion. The subsequent activation of K(+) channels terminates secretion. We examined whether KCNQ1 channels are expressed in pancreatic beta-cells and analysed their functional role. Using RT/PCR cellular mRNA of KCNQ1 but not of KCNE1 channels was detected in INS-1 cells. Effects of two sulfonamide analogues, 293B and HMR1556, inhibitors of KCNQ1 channels, were examined on voltage-activated outwardly rectifying K(+) currents using the patch-clamp method. It was found that 293B inhibited 60% of whole-cell outward currents induced by voltage pulses from -70 to +50 mV with a concentration for half-maximal inhibition (IC(50)) of 37 microM. The other sulfonamide analogue HMR1556 inhibited 48% of the outward current with an IC(50) of 7 microM. The chromanol 293B had no effect on tolbutamide-sensitive K(ATP) channels. Action potentials induced by current injections were broadened and after-repolarisation was attenuated by 293B. Insulin secretion in the presence but not in the absence of tolbutamide was significantly increased by 293B. These results suggest that 293B- and HMR1556-sensitive channels, probably in concert with other voltage-activated K(+) channels, influence action potential duration and frequency and thus insulin secretion.

  1. Key proteins involved in insulin vesicle exocytosis and secretion

    PubMed Central

    Xiong, Qian-Yin; Yu, Cui; Zhang, Yao; Ling, Liefeng; Wang, Lizhuo; Gao, Jia-Lin

    2017-01-01

    In vivo insulin secretion is predominantly affected by blood glucose concentration, blood concentration of amino acids, gastrointestinal hormones and free nerve functional status, in addition to other factors. Insulin is one of the most important hormones in the body, and its secretion is precisely controlled by nutrients, neurotransmitters and hormones. The insulin exocytosis process is similar to the neurotransmitter release mechanism. There are various types of proteins and lipids that participate in the insulin secretory vesicle fusion process, such as soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein, Ras-related proteins and vacuolar-type H+-ATPase (V-ATPase). Notably, the SNARE protein is the molecular basis of exocytotic activity. In the current review, the role of the vesicle membrane proteins (synaptobrevins, vesicle associated membrane proteins and target membrane proteins) and auxiliary proteins (Rab proteins and Munc-18 proteins) in vesicle fusion activity were summarized. A summary of these key proteins involved in insulin granule secretion will facilitate understanding of the pathogenesis of diabetes. PMID:28357064

  2. Role of Vitamin D in Insulin Secretion and Insulin Sensitivity for Glucose Homeostasis

    PubMed Central

    Alvarez, Jessica A.; Ashraf, Ambika

    2010-01-01

    Vitamin D functions are not limited to skeletal health benefits and may extend to preservation of insulin secretion and insulin sensitivity. This review summarizes the literature related to potential vitamin D influences on glucose homeostasis and insulin sensitivity. Cross-sectional data provide some evidence that circulating 25-hydroxyvitamin D (25(OH)D) is inversely associated with insulin resistance, although direct measurements of insulin sensitivity are required for confirmation. Reported associations with insulin secretion, however, are contradictory. Available prospective studies support a protective influence of high 25(OH)D concentrations on type 2 diabetes mellitus risk. There is a general lack of consistency in vitamin D intervention outcomes on insulin secretion and sensitivity, likely due to differences in subject populations, length of interventions, and forms of vitamin D supplementation. Vitamin D receptor gene polymorphisms and vitamin D interactions with the insulin like growth factor system may further influence glucose homeostasis. The ambiguity of optimal vitamin D dosing regimens and optimal therapeutic concentrations of serum 25(OH)D limit available intervention studies. Future studies, including cross-sectional and prospective, should be performed in populations at high risk for both vitamin D deficiency and type 2 diabetes mellitus. Well-designed, placebo-controlled, randomized intervention studies are required to establish a true protective influence of vitamin D on glucose homeostasis. PMID:20011094

  3. Role of vitamin d in insulin secretion and insulin sensitivity for glucose homeostasis.

    PubMed

    Alvarez, Jessica A; Ashraf, Ambika

    2010-01-01

    Vitamin D functions are not limited to skeletal health benefits and may extend to preservation of insulin secretion and insulin sensitivity. This review summarizes the literature related to potential vitamin D influences on glucose homeostasis and insulin sensitivity. Cross-sectional data provide some evidence that circulating 25-hydroxyvitamin D (25(OH)D) is inversely associated with insulin resistance, although direct measurements of insulin sensitivity are required for confirmation. Reported associations with insulin secretion, however, are contradictory. Available prospective studies support a protective influence of high 25(OH)D concentrations on type 2 diabetes mellitus risk. There is a general lack of consistency in vitamin D intervention outcomes on insulin secretion and sensitivity, likely due to differences in subject populations, length of interventions, and forms of vitamin D supplementation. Vitamin D receptor gene polymorphisms and vitamin D interactions with the insulin like growth factor system may further influence glucose homeostasis. The ambiguity of optimal vitamin D dosing regimens and optimal therapeutic concentrations of serum 25(OH)D limit available intervention studies. Future studies, including cross-sectional and prospective, should be performed in populations at high risk for both vitamin D deficiency and type 2 diabetes mellitus. Well-designed, placebo-controlled, randomized intervention studies are required to establish a true protective influence of vitamin D on glucose homeostasis.

  4. A genetic strategy to measure circulating Drosophila insulin reveals genes regulating insulin production and secretion.

    PubMed

    Park, Sangbin; Alfa, Ronald W; Topper, Sydni M; Kim, Grace E S; Kockel, Lutz; Kim, Seung K

    2014-08-01

    Insulin is a major regulator of metabolism in metazoans, including the fruit fly Drosophila melanogaster. Genome-wide association studies (GWAS) suggest a genetic basis for reductions of both insulin sensitivity and insulin secretion, phenotypes commonly observed in humans with type 2 diabetes mellitus (T2DM). To identify molecular functions of genes linked to T2DM risk, we developed a genetic tool to measure insulin-like peptide 2 (Ilp2) levels in Drosophila, a model organism with superb experimental genetics. Our system permitted sensitive quantification of circulating Ilp2, including measures of Ilp2 dynamics during fasting and re-feeding, and demonstration of adaptive Ilp2 secretion in response to insulin receptor haploinsufficiency. Tissue specific dissection of this reduced insulin signaling phenotype revealed a critical role for insulin signaling in specific peripheral tissues. Knockdown of the Drosophila orthologues of human T2DM risk genes, including GLIS3 and BCL11A, revealed roles of these Drosophila genes in Ilp2 production or secretion. Discovery of Drosophila mechanisms and regulators controlling in vivo insulin dynamics should accelerate functional dissection of diabetes genetics.

  5. Somatostatin-secreting Pheochromocytoma Mimicking Insulin-dependent Diabetes Mellitus

    PubMed Central

    Hirai, Hiroyuki; Midorikawa, Sanae; Suzuki, Shinichi; Sasano, Hironobu; Watanabe, Tsuyoshi; Satoh, Hiroaki

    2016-01-01

    We herein present the findings of a 42-year-old woman with either adrenal pheochromocytoma or intraadrenal paraganglioma that simultaneously secreted somatostatin, thus mimicking insulin-dependent diabetes mellitus. Pheochromocytoma was clinically diagnosed based on scintigraphy, elevated catecholamine levels, and finally a histopathological analysis of resected specimens. The patient had diabetic ketosis, requiring 40 U insulin for treatment. Following laparoscopic adrenalectomy, insulin therapy was discontinued and the urinary c-peptide levels changed from 5.5-9.0 to 81.3-87.0 μg/day. Histologically, somatostatin immunoreactivity was detected and the somatostatin levels were elevated in the serum-like fluid obtained from the tumor. Clinicians should be aware of the possible occurrence of simultaneous ectopic hormone secretion in patients with pheochromocytoma. PMID:27746437

  6. Somatostatin-secreting Pheochromocytoma Mimicking Insulin-dependent Diabetes Mellitus.

    PubMed

    Hirai, Hiroyuki; Midorikawa, Sanae; Suzuki, Shinichi; Sasano, Hironobu; Watanabe, Tsuyoshi; Satoh, Hiroaki

    We herein present the findings of a 42-year-old woman with either adrenal pheochromocytoma or intraadrenal paraganglioma that simultaneously secreted somatostatin, thus mimicking insulin-dependent diabetes mellitus. Pheochromocytoma was clinically diagnosed based on scintigraphy, elevated catecholamine levels, and finally a histopathological analysis of resected specimens. The patient had diabetic ketosis, requiring 40 U insulin for treatment. Following laparoscopic adrenalectomy, insulin therapy was discontinued and the urinary c-peptide levels changed from 5.5-9.0 to 81.3-87.0 μg/day. Histologically, somatostatin immunoreactivity was detected and the somatostatin levels were elevated in the serum-like fluid obtained from the tumor. Clinicians should be aware of the possible occurrence of simultaneous ectopic hormone secretion in patients with pheochromocytoma.

  7. Antrodia camphorata Increases Insulin Secretion and Protects from Apoptosis in MIN6 Cells

    PubMed Central

    Vong, Chi Teng; Tseng, Hisa Hui Ling; Kwan, Yiu Wa; Lee, Simon Ming-Yuen; Hoi, Maggie Pui Man

    2016-01-01

    Antrodia camphorata is a Taiwanese-specific fungus which has been used clinically to treat hypertension, immune- and liver-related diseases and cancer; however, it has never been studied in type 2 diabetes mellitus (T2DM). Hyperglycemia in T2DM causes endoplasmic reticulum (ER) stress, leading to β-cell dysfunction. During chronic ER stress, misfolded proteins accumulate and initiate β-cell apoptosis. Moreover, β-cell dysfunction leads to defect in insulin secretion, which is the key process in the development and progression of T2DM. Therefore, the aim of the present study was to examine the effects of A. camphorata on insulin secretion and ER stress-induced apoptosis in a mouse β-cell line, MIN6, and their underlying mechanisms. We demonstrated that the ethanolic extract of A. camphorata increased glucose-induced insulin secretion dose-dependently through peroxisome proliferator-activated receptor-γ (PPAR-γ) pathway, and upregulated genes that were involved in insulin secretion, including PPAR-γ, glucose transporter-2 and glucokinase. Furthermore, A. camphorata slightly increased cell proliferation, as well as protected from ER stress-induced apoptosis in MIN6 cells. In conclusion, this study provided evidences that A. camphorata might have anti-diabetic effects and could be a novel drug for T2DM. PMID:27047382

  8. Antrodia camphorata Increases Insulin Secretion and Protects from Apoptosis in MIN6 Cells.

    PubMed

    Vong, Chi Teng; Tseng, Hisa Hui Ling; Kwan, Yiu Wa; Lee, Simon Ming-Yuen; Hoi, Maggie Pui Man

    2016-01-01

    Antrodia camphorata is a Taiwanese-specific fungus which has been used clinically to treat hypertension, immune- and liver-related diseases and cancer; however, it has never been studied in type 2 diabetes mellitus (T2DM). Hyperglycemia in T2DM causes endoplasmic reticulum (ER) stress, leading to β-cell dysfunction. During chronic ER stress, misfolded proteins accumulate and initiate β-cell apoptosis. Moreover, β-cell dysfunction leads to defect in insulin secretion, which is the key process in the development and progression of T2DM. Therefore, the aim of the present study was to examine the effects of A. camphorata on insulin secretion and ER stress-induced apoptosis in a mouse β-cell line, MIN6, and their underlying mechanisms. We demonstrated that the ethanolic extract of A. camphorata increased glucose-induced insulin secretion dose-dependently through peroxisome proliferator-activated receptor-γ (PPAR-γ) pathway, and upregulated genes that were involved in insulin secretion, including PPAR-γ, glucose transporter-2 and glucokinase. Furthermore, A. camphorata slightly increased cell proliferation, as well as protected from ER stress-induced apoptosis in MIN6 cells. In conclusion, this study provided evidences that A. camphorata might have anti-diabetic effects and could be a novel drug for T2DM.

  9. Growth hormone (GH) secretory dynamics in a case of acromegalic gigantism associated with hyperprolactinemia: nonpulsatile secretion of GH may induce elevated insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 levels.

    PubMed

    Yoshida, T; Shimatsu, A; Sakane, N; Hizuka, N; Horikawa, R; Tanaka, T

    1996-01-01

    We describe a case of pituitary gigantism with low levels of growth hormone (GH), elevated insulin-like growth factor-I (IGF-I), and IGF-binding protein-3 (IGF-BP-3). The patient had characteristic clinical features of gigantism and acromegaly. The basal serum GH levels ranged from 1.2-1.9 micrograms/L, which were considered to be within normal limits. Serum GH response to either insulin-induced hypoglycemia or GH-releasing hormone was blunted. Frequent blood samplings during daytime and at night showed nonpulsatile GH secretion. Serum prolactin, IGF-I and IGF-binding protein-3 levels were elevated. After unsuccessful surgery, bromocryptine treatment normalized serum prolactin without affecting serum GH and IGF-I levels. Combined administration of octreotide and bromocryptine reduced serum GH and IGF-I levels. GH bioactivity as measured by Nb2 cell proliferation assay was within reference range. In the present case, nonpulsatile GH secretion and enhanced tissue sensitivity to GH may induce hypersecretion of IGF-I and IGF-BP-3 and cause clinical acromegalic gigantism.

  10. Impaired insulin secretion increases the risk of Alzheimer disease.

    PubMed

    Rönnemaa, E; Zethelius, B; Sundelöf, J; Sundström, J; Degerman-Gunnarsson, M; Berne, C; Lannfelt, L; Kilander, L

    2008-09-30

    Subjects with diabetes are reported to have an increased risk of dementia and cognitive impairment. However, the underlying causes remain unknown. We investigated the longitudinal associations between midlife insulin secretion, glucose metabolism, and the subsequent development of Alzheimer disease (AD) and dementia. The population-based Uppsala Longitudinal Study of Adult Men started 1970 when the 2,322 participants were 50 years old. Investigation at baseline included determinations of acute insulin response and glucose tolerance using the IV glucose tolerance test and Homeostasis Model Assessment insulin resistance index. During a median follow up of 32 years, 102 participants were diagnosed with AD, 57 with vascular dementia, and 394 with any dementia or cognitive impairment. Associations were analyzed using Cox proportional hazard models. A low insulin response at baseline was associated with a higher cumulative risk of AD (hazard ratio for 1 SD decrease, 1.31; 95% CI, 1.10-1.56) also after adjustment for age, systolic blood pressure, body mass index, serum cholesterol, smoking, education level, and insulin resistance. This association was stronger in subjects without the APOE epsilon4 allele. Impaired glucose tolerance increased the risk of vascular dementia (hazard ratio for 1 SD decrease, 1.45; 95% CI, 1.05-2.00) but not AD. Impaired insulin secretion, glucose intolerance, and estimates of insulin resistance were all associated with higher risk of any dementia and cognitive impairment. In this longitudinal study, impaired acute insulin response at midlife was associated with an increased risk of Alzheimer disease (AD) up to 35 years later suggesting a causal link between insulin metabolism and the pathogenesis of AD.

  11. Dynamin 2 regulates biphasic insulin secretion and plasma glucose homeostasis

    PubMed Central

    Fan, Fan; Ji, Chen; Wu, Yumei; Ferguson, Shawn M.; Tamarina, Natalia; Philipson, Louis H.; Lou, Xuelin

    2015-01-01

    Alterations in insulin granule exocytosis and endocytosis are paramount to pancreatic β cell dysfunction in diabetes mellitus. Here, using temporally controlled gene ablation specifically in β cells in mice, we identified an essential role of dynamin 2 GTPase in preserving normal biphasic insulin secretion and blood glucose homeostasis. Dynamin 2 deletion in β cells caused glucose intolerance and substantial reduction of the second phase of glucose-stimulated insulin secretion (GSIS); however, mutant β cells still maintained abundant insulin granules, with no signs of cell surface expansion. Compared with control β cells, real-time capacitance measurements demonstrated that exocytosis-endocytosis coupling was less efficient but not abolished; clathrin-mediated endocytosis (CME) was severely impaired at the step of membrane fission, which resulted in accumulation of clathrin-coated endocytic intermediates on the plasma membrane. Moreover, dynamin 2 ablation in β cells led to striking reorganization and enhancement of actin filaments, and insulin granule recruitment and mobilization were impaired at the later stage of GSIS. Together, our results demonstrate that dynamin 2 regulates insulin secretory capacity and dynamics in vivo through a mechanism depending on CME and F-actin remodeling. Moreover, this study indicates a potential pathophysiological link between endocytosis and diabetes mellitus. PMID:26413867

  12. Glutamate Acts as a Key Signal Linking Glucose Metabolism to Incretin/cAMP Action to Amplify Insulin Secretion

    PubMed Central

    Gheni, Ghupurjan; Ogura, Masahito; Iwasaki, Masahiro; Yokoi, Norihide; Minami, Kohtaro; Nakayama, Yasumune; Harada, Kazuo; Hastoy, Benoit; Wu, Xichen; Takahashi, Harumi; Kimura, Kazushi; Matsubara, Toshiya; Hoshikawa, Ritsuko; Hatano, Naoya; Sugawara, Kenji; Shibasaki, Tadao; Inagaki, Nobuya; Bamba, Takeshi; Mizoguchi, Akira; Fukusaki, Eiichiro; Rorsman, Patrik; Seino, Susumu

    2014-01-01

    Summary Incretins, hormones released by the gut after meal ingestion, are essential for maintaining systemic glucose homeostasis by stimulating insulin secretion. The effect of incretins on insulin secretion occurs only at elevated glucose concentrations and is mediated by cAMP signaling, but the mechanism linking glucose metabolism and cAMP action in insulin secretion is unknown. We show here, using a metabolomics-based approach, that cytosolic glutamate derived from the malate-aspartate shuttle upon glucose stimulation underlies the stimulatory effect of incretins and that glutamate uptake into insulin granules mediated by cAMP/PKA signaling amplifies insulin release. Glutamate production is diminished in an incretin-unresponsive, insulin-secreting β cell line and pancreatic islets of animal models of human diabetes and obesity. Conversely, a membrane-permeable glutamate precursor restores amplification of insulin secretion in these models. Thus, cytosolic glutamate represents the elusive link between glucose metabolism and cAMP action in incretin-induced insulin secretion. PMID:25373904

  13. Rab2A is a pivotal switch protein that promotes either secretion or ER-associated degradation of (pro)insulin in insulin-secreting cells

    PubMed Central

    Sugawara, Taichi; Kano, Fumi; Murata, Masayuki

    2014-01-01

    Rab2A, a small GTPase localizing to the endoplasmic reticulum (ER)-Golgi intermediate compartment (ERGIC), regulates COPI-dependent vesicular transport from the ERGIC. Rab2A knockdown inhibited glucose-stimulated insulin secretion and concomitantly enlarged the ERGIC in insulin-secreting cells. Large aggregates of polyubiquitinated proinsulin accumulated in the cytoplasmic vicinity of a unique large spheroidal ERGIC, designated the LUb-ERGIC. Well-known components of ER-associated degradation (ERAD) also accumulated at the LUb-ERGIC, creating a suitable site for ERAD-mediated protein quality control. Moreover, chronically high glucose levels, which induced the enlargement of the LUb-ERGIC and ubiquitinated protein aggregates, impaired Rab2A activity by promoting dissociation from its effector, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), in response to poly (ADP-ribosyl)ation of GAPDH. The inactivation of Rab2A relieved glucose-induced ER stress and inhibited ER stress-induced apoptosis. Collectively, these results suggest that Rab2A is a pivotal switch that controls whether insulin should be secreted or degraded at the LUb-ERGIC and Rab2A inactivation ensures alleviation of ER stress and cell survival under chronic glucotoxicity. PMID:25377857

  14. Dynamics of insulin secretion and the clinical implications for obesity and diabetes

    PubMed Central

    Seino, Susumu; Shibasaki, Tadao; Minami, Kohtaro

    2011-01-01

    Insulin secretion is a highly dynamic process regulated by various factors including nutrients, hormones, and neuronal inputs. The dynamics of insulin secretion can be studied at different levels: the single β cell, pancreatic islet, whole pancreas, and the intact organism. Studies have begun to analyze cellular and molecular mechanisms underlying dynamics of insulin secretion. This review focuses on our current understanding of the dynamics of insulin secretion in vitro and in vivo and discusses their clinical relevance. PMID:21633180

  15. Defective insulin secretion by chronic glucagon receptor activation in glucose intolerant mice.

    PubMed

    Ahlkvist, Linda; Omar, Bilal; Valeur, Anders; Fosgerau, Keld; Ahrén, Bo

    2016-03-01

    Stimulation of insulin secretion by short-term glucagon receptor (GCGR) activation is well characterized; however, the effect of long-term GCGR activation on β-cell function is not known, but of interest, since hyperglucagonemia occurs early during development of type 2 diabetes. Therefore, we examined whether chronic GCGR activation affects insulin secretion in glucose intolerant mice. To induce chronic GCGR activation, high-fat diet fed mice were continuously (2 weeks) infused with the stable glucagon analog ZP-GA-1 and challenged with oral glucose and intravenous glucose±glucagon-like peptide 1 (GLP1). Islets were isolated to evaluate the insulin secretory response to glucose±GLP1 and their pancreas were collected for immunohistochemical analysis. Two weeks of ZP-GA-1 infusion reduced insulin secretion both after oral and intravenous glucose challenges in vivo and in isolated islets. These inhibitory effects were corrected for by GLP1. Also, we observed increased β-cell area and islet size. We conclude that induction of chronic ZP-GA-1 levels in glucose intolerant mice markedly reduces insulin secretion, and thus, we suggest that chronic activation of the GCGR may contribute to the failure of β-cell function during development of type 2 diabetes.

  16. Association between Higher Serum Cortisol Levels and Decreased Insulin Secretion in a General Population

    PubMed Central

    Kamba, Aya; Daimon, Makoto; Murakami, Hiroshi; Otaka, Hideyuki; Matsuki, Kota; Sato, Eri; Tanabe, Jutaro; Takayasu, Shinobu; Matsuhashi, Yuki; Yanagimachi, Miyuki; Terui, Ken; Kageyama, Kazunori; Tokuda, Itoyo; Takahashi, Ippei; Nakaji, Shigeyuki

    2016-01-01

    Glucocorticoids (GCs) are well known to induce insulin resistance. However, the effect of GCs on insulin secretion has not been well characterized under physiological conditions in human. We here evaluated the effect of GCs on insulin secretion/ß-cell function precisely in a physiological condition. A population-based study of 1,071 Japanese individuals enrolled in the 2014 Iwaki study (390 men, 681 women; aged 54.1 ± 15.1 years), those excluded individuals taking medication for diabetes or steroid treatment, were enrolled in the present study. Association between serum cortisol levels and insulin resistance/secretion assessed by homeostasis model assessment using fasting blood glucose and insulin levels (HOMA-R and HOMA-ß, respectively) were examined. Univariate linear regression analyses showed correlation of serum cortisol levels with HOMA-ß (ß = -0.134, p <0.001) but not with HOMA-R (ß = 0.042, p = 0.172). Adjustments for age, gender, and the multiple clinical characteristics correlated with HOMA indices showed similar results (HOMA-ß: ß = -0.062, p = 0.025; HOMA-R: ß = -0.023, p = 0.394). The correlation between serum cortisol levels and HOMA-ß remained significant after adjustment for HOMA- R (ß = -0.057, p = 0.034). When subjects were tertiled based on serum cortisol levels, the highest tertile was at greater risk of decreased insulin secretion (defined as lower one third of HOMA-ß (≤70)) than the lowest tertile, after adjustment for multiple factors including HOMA- R (odds ratio 1.26, 95% confidence interval 1.03–1.54). In conclusion, higher serum cortisol levels are significantly associated with decreased insulin secretion in the physiological cortisol range in a Japanese population. PMID:27861636

  17. Methylated trivalent arsenicals are potent inhibitors of glucose stimulated insulin secretion by murine pancreatic islets

    SciTech Connect

    Douillet, Christelle; Currier, Jenna; Saunders, Jesse; Bodnar, Wanda M.; Matoušek, Tomáš; Stýblo, Miroslav

    2013-02-15

    Epidemiologic evidence has linked chronic exposure to inorganic arsenic (iAs) with an increased prevalence of diabetes mellitus. Laboratory studies have identified several mechanisms by which iAs can impair glucose homeostasis. We have previously shown that micromolar concentrations of arsenite (iAs{sup III}) or its methylated trivalent metabolites, methylarsonite (MAs{sup III}) and dimethylarsinite (DMAs{sup III}), inhibit the insulin-activated signal transduction pathway, resulting in insulin resistance in adipocytes. Our present study examined effects of the trivalent arsenicals on insulin secretion by intact pancreatic islets isolated from C57BL/6 mice. We found that 48-hour exposures to low subtoxic concentrations of iAs{sup III}, MAs{sup III} or DMAs{sup III} inhibited glucose-stimulated insulin secretion (GSIS), but not basal insulin secretion. MAs{sup III} and DMAs{sup III} were more potent than iAs{sup III} as GSIS inhibitors with estimated IC{sub 50} ≤ 0.1 μM. The exposures had little or no effects on insulin content of the islets or on insulin expression, suggesting that trivalent arsenicals interfere with mechanisms regulating packaging of the insulin transport vesicles or with translocation of these vesicles to the plasma membrane. Notably, the inhibition of GSIS by iAs{sup III}, MAs{sup III} or DMAs{sup III} could be reversed by a 24-hour incubation of the islets in arsenic-free medium. These results suggest that the insulin producing pancreatic β-cells are among the targets for iAs exposure and that the inhibition of GSIS by low concentrations of the methylated metabolites of iAs may be the key mechanism of iAs-induced diabetes. - Highlights: ► Trivalent arsenicals inhibit glucose stimulated insulin secretion by pancreatic islets. ► MAs{sup III} and DMAs{sup III} are more potent inhibitors than arsenite with IC{sub 50} ∼ 0.1 μM. ► The arsenicals have little or no effects on insulin expression in pancreatic islets. ► The inhibition of

  18. Glucagon-like peptide 1 and fatty acids amplify pulsatile insulin secretion from perifused rat islets.

    PubMed Central

    Cunningham, Barbara A; Richard, Ann-Marie T; Dillon, Joseph S; Daley, Jennifer T; Civelek, Vildan N; Deeney, Jude T; Yaney, Gordon C; Corkey, Barbara E; Tornheim, Keith

    2003-01-01

    Glucose-induced insulin secretion from isolated, perifused rat islets is pulsatile with a period of about 5-10 min, similar to the insulin oscillations that are seen in healthy humans but which are impaired in Type II diabetes. We evaluated the pattern of enhancement by the potent incretin, glucagon-like peptide 1 (GLP-1). GLP-1 increased the amplitude of pulses and the magnitude of insulin secretion from the perifused islets, without affecting the average time interval between pulses. Forskolin and the phosphodiesterase inhibitor isobutylmethylxanthine had the same effect, suggesting that the effect was due to elevated cAMP levels. The possibility that cAMP might enhance the amplitude of pulses by reducing phosphofructo-2-kinase (PFK-2) activity was eliminated when the liver isoform of PFK-2 was shown to be absent from beta-cells. The possibility that cAMP enhanced pulsatile secretion, at least in part, by stimulating lipolysis was supported by the observations that added oleate had a similar effect on secretion, and that the incretin effect of GLP-1 was inhibited by the lipase inhibitor orlistat. These data show that the physiological incretin GLP-1 preserves and enhances normal pulsatile insulin secretion, which may be essential in proposed therapeutic uses of GLP-1 or its analogues. PMID:12356335

  19. Reevaluation of Fatty Acid Receptor 1 as a Drug Target for the Stimulation of Insulin Secretion in Humans

    PubMed Central

    Wagner, Robert; Kaiser, Gabriele; Gerst, Felicia; Christiansen, Elisabeth; Due-Hansen, Maria E.; Grundmann, Manuel; Machicao, Fausto; Peter, Andreas; Kostenis, Evi; Ulven, Trond; Fritsche, Andreas; Häring, Hans-Ulrich; Ullrich, Susanne

    2013-01-01

    The role of free fatty acid receptor 1 (FFAR1/GPR40) in glucose homeostasis is still incompletely understood. Small receptor agonists stimulating insulin secretion are undergoing investigation for the treatment of type 2 diabetes. Surprisingly, genome-wide association studies did not discover diabetes risk variants in FFAR1. We reevaluated the role of FFAR1 in insulin secretion using a specific agonist, FFAR1-knockout mice and human islets. Nondiabetic individuals were metabolically phenotyped and genotyped. In vitro experiments indicated that palmitate and a specific FFAR1 agonist, TUG-469, stimulate glucose-induced insulin secretion through FFAR1. The proapoptotic effect of chronic exposure of β-cells to palmitate was independent of FFAR1. TUG-469 was protective, whereas inhibition of FFAR1 promoted apoptosis. In accordance with the proapoptotic effect of palmitate, in vivo cross-sectional observations demonstrated a negative association between fasting free fatty acids (NEFAs) and insulin secretion. Because NEFAs stimulate secretion through FFAR1, we examined the interaction of genetic variation in FFAR1 with NEFA and insulin secretion. The inverse association of NEFA and secretion was modulated by rs1573611 and became steeper for carriers of the minor allele. In conclusion, FFAR1 agonists support β-cell function, but variation in FFAR1 influences NEFA effects on insulin secretion and therefore could affect therapeutic efficacy of FFAR1 agonists. PMID:23378609

  20. Cadherin engagement improves insulin secretion of single human β-cells.

    PubMed

    Parnaud, Geraldine; Lavallard, Vanessa; Bedat, Benoît; Matthey-Doret, David; Morel, Philippe; Berney, Thierry; Bosco, Domenico

    2015-03-01

    The aim of this study was to assess whether cadherin-mediated adhesion of human islet cells was affected by insulin secretagogues and explore the role of cadherins in the secretory activity of β-cells. Experiments were carried out with single islet cells adherent to chimeric proteins made of functional E-, N-, or P-cadherin ectodomains fused to the Fc fragment of immunoglobulin (E-cad/Fc, N-cad/Fc, and P-cad/Fc) and immobilized on an inert substrate. We observed that cadherin expression in islet cells was not affected by insulin secretagogues. Adhesion tests showed that islet cells attached to N-cad/Fc and E-cad/Fc acquired, in a time- and secretagogue-dependent manner, a spreading form that was inhibited by blocking cadherin antibodies. By reverse hemolytic plaque assay, we showed that glucose-stimulated insulin secretion of single β-cells was increased by N-cad/Fc and E-cad/Fc adhesion compared with control. In the presence of E-cad/Fc and after glucose stimulation, we showed that total insulin secretion was six times higher in spreading β-cells compared with round β-cells. Furthermore, cadherin-mediated adhesion induced an asymmetric distribution of cortical actin in β-cells. Our results demonstrate that adhesion of β-cells to E- and N-cadherins is regulated by insulin secretagogues and that E- and N-cadherin engagement promotes stimulated insulin secretion.

  1. Regulation of serum potassium during insulin-induced hypoglycemia.

    PubMed

    Petersen, K G; Schlüter, K J; Kerp, L

    1982-07-01

    Counterregulatory secretion of epinephrine occurs during severe insulin-induced hypoglycemia. Under these conditions (minimal plasma glucose 27.4 +/- 1 mg/dl) the decrease of serum potassium concentration (0.9 mVal/L) is mediated by two mechanisms: insulin-induced (0.48 mVal/L) and epinephrine-induced (0.42 mVal/L) cellular uptake of potassium. Epinephrine-induced serum potassium uptake appears to be more sensitive to beta-adrenoceptor blockade than glucose production. The intensification of insulin-induced hypokalemia by epinephrine is of clinical significance.

  2. Dual Effect of Rosuvastatin on Glucose Homeostasis Through Improved Insulin Sensitivity and Reduced Insulin Secretion.

    PubMed

    Salunkhe, Vishal A; Mollet, Inês G; Ofori, Jones K; Malm, Helena A; Esguerra, Jonathan L S; Reinbothe, Thomas M; Stenkula, Karin G; Wendt, Anna; Eliasson, Lena; Vikman, Jenny

    2016-08-01

    Statins are beneficial in the treatment of cardiovascular disease (CVD), but these lipid-lowering drugs are associated with increased incidence of new on-set diabetes. The cellular mechanisms behind the development of diabetes by statins are elusive. Here we have treated mice on normal diet (ND) and high fat diet (HFD) with rosuvastatin. Under ND rosuvastatin lowered blood glucose through improved insulin sensitivity and increased glucose uptake in adipose tissue. In vitro rosuvastatin reduced insulin secretion and insulin content in islets. In the beta cell Ca(2+) signaling was impaired and the density of granules at the plasma membrane was increased by rosuvastatin treatment. HFD mice developed insulin resistance and increased insulin secretion prior to administration of rosuvastatin. Treatment with rosuvastatin decreased the compensatory insulin secretion and increased glucose uptake. In conclusion, our data shows dual effects on glucose homeostasis by rosuvastatin where insulin sensitivity is improved, but beta cell function is impaired. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

  3. Iron stores, blood donation, and insulin sensitivity and secretion.

    PubMed

    Fernández-Real, José Manuel; López-Bermejo, Abel; Ricart, Wifredo

    2005-07-01

    Epidemiologists have observed that blood donation is associated with decreased risk of type 2 diabetes and cardiovascular disease. We investigated the relationship between iron stores and insulin sensitivity, after controlling for known confounding factors, and compared insulin sensitivity between blood donors and individuals who had never donated blood (nondonors). In 181 men, insulin sensitivity and insulin secretion were evaluated through frequently sampled intravenous glucose tolerance tests with minimal model analysis. Men who donated blood between 6 months and 5 years before inclusion (n = 21) were carefully matched with nondonors (n = 66) for age, body mass index, waist-to-hip ratio, and cardiovascular risk profile, including blood lipids, blood pressure, and smoking status. Frequent blood donors (2-10 donations) had increased insulin sensitivity [3.42 (1.03) vs 2.45 (1.2) x 10(-4) x min(-1) x mIU/L; P = 0.04], decreased insulin secretion [186 (82) vs 401.7 (254) mIU/L x min; P <0.0001], and significantly lower iron stores [serum ferritin, 101.5 (74) vs 162 (100) microg/L; P = 0.017] than nondonors, but the 2 groups had similar blood hematocrits and blood hemoglobin concentrations. Blood donation is simultaneously associated with increased insulin sensitivity and decreased iron stores. Stored iron seems to impact negatively on insulin action even in healthy people, and not just in classic pathologic conditions associated with iron overload (hemochromatosis and hemosiderosis). According to these observations, it is imperative that a definition of excessive iron stores in healthy people be formulated.

  4. Signalling satiety and starvation to β-Cell insulin secretion.

    PubMed

    Holness, Mark J; Hegazy, Sharif; Sugden, Mary C

    2011-09-01

    The impact of bariatric surgery on insulin sensitivity and glucose tolerance has refocused interest in the role of gut-derived factors in the regulation of insulin secretion and action. The incretins, glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide-1 (GLP-1) are released from endocrine cells in the small intestinal mucosa primarily in response to oral nutrient ingestion. They have various effects, including augmentation of glucose-stimulated insulin secretion (GSIS), actions that promote the cellular assimilation and storage of dietary glucose and lipid as liver and skeletal muscle glycogen and adipocyte triacylglycerol (TAG) respectively. Similarly, increased delivery of fatty acids (FA) acutely augments GSIS, and the resultant enhancement of GSIS facilitates FA storage as adipocyte TAG. Leptin secretion from white adipocytes curbs appetite to limit dietary nutrient intake and adipocyte TAG storage and, potentially, GSIS, thereby curtailing insulin-dependent TAG storage. On fasting, GSIS is curbed, an effect the mechanism of which is even now incompletely understood, but which may reflect augmented β-cell FA oxidation. The orexigen ghrelin, systemic concentrations of which increase with fasting, exerts enigmatic effects on GSIS, in that acylated ghrelin and unacylated ghrelin exert opposing effects on GSIS, whereas acylated ghrelin and unacylated ghrelin share protective effects on islet survival. This review will build on these emerging studies to evaluate the roles of the incretins, leptin, lipids and acylated and unacylated ghrelin in modulating islet function and survival during feasting and fasting.

  5. Exposure to static magnetic fields increases insulin secretion in rat INS-1 cells by activating the transcription of the insulin gene and up-regulating the expression of vesicle-secreted proteins.

    PubMed

    Mao, Libin; Wang, Huiqin; Ma, Fenghui; Guo, Zhixia; He, Hongpeng; Zhou, Hao; Wang, Nan

    2017-08-01

    To evaluate the effect of static magnetic fields (SMFs) on insulin secretion and explore the mechanisms underlying exposure to SMF-induced insulin secretion in rat insulinoma INS-1 cells. INS-1 cells were exposed to a 400 mT SMF for 72 h, and the proliferation of INS-1 cells was detected by (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The secretion of insulin was measured with an enzyme linked immunosorbent assays (ELISA), the expression of genes was detected by real-time PCR, and the expression of proteins was measured by Western blotting. Exposure to an SMF increased the expression and secretion of insulin by INS-1 cells but did not affect cell proliferation. Moreover, SMF exposure up-regulated the expression of several pancreas-specific transcriptional factors. Specifically, the activity of the rat insulin promoter was enhanced in INS-1 cells exposed to an SMF, and the expression levels of synaptosomal-associated protein 25 (SNAP-25) and syntaxin-1A were up-regulated after exposure to an SMF. SMF exposure can promote insulin secretion in rat INS-1 cells by activating the transcription of the insulin gene and up-regulating the expression of vesicle-secreted proteins.

  6. A Novel GLP1 Receptor Interacting Protein ATP6ap2 Regulates Insulin Secretion in Pancreatic Beta Cells.

    PubMed

    Dai, Feihan F; Bhattacharjee, Alpana; Liu, Ying; Batchuluun, Battsetseg; Zhang, Ming; Wang, Xinye Serena; Huang, Xinyi; Luu, Lemieux; Zhu, Dan; Gaisano, Herbert; Wheeler, Michael B

    2015-10-09

    GLP1 activates its receptor, GLP1R, to enhance insulin secretion. The activation and transduction of GLP1R requires complex interactions with a host of accessory proteins, most of which remain largely unknown. In this study, we used membrane-based split ubiquitin yeast two-hybrid assays to identify novel GLP1R interactors in both mouse and human islets. Among these, ATP6ap2 (ATPase H(+)-transporting lysosomal accessory protein 2) was identified in both mouse and human islet screens. ATP6ap2 was shown to be abundant in islets including both alpha and beta cells. When GLP1R and ATP6ap2 were co-expressed in beta cells, GLP1R was shown to directly interact with ATP6ap2, as assessed by co-immunoprecipitation. In INS-1 cells, overexpression of ATP6ap2 did not affect insulin secretion; however, siRNA knockdown decreased both glucose-stimulated and GLP1-induced insulin secretion. Decreases in GLP1-induced insulin secretion were accompanied by attenuated GLP1 stimulated cAMP accumulation. Because ATP6ap2 is a subunit required for V-ATPase assembly of insulin granules, it has been reported to be involved in granule acidification. In accordance with this, we observed impaired insulin granule acidification upon ATP6ap2 knockdown but paradoxically increased proinsulin secretion. Importantly, as a GLP1R interactor, ATP6ap2 was required for GLP1-induced Ca(2+) influx, in part explaining decreased insulin secretion in ATP6ap2 knockdown cells. Taken together, our findings identify a group of proteins that interact with the GLP1R. We further show that one interactor, ATP6ap2, plays a novel dual role in beta cells, modulating both GLP1R signaling and insulin processing to affect insulin secretion.

  7. Apolipoprotein A-I interactions with insulin secretion and production.

    PubMed

    Rye, Kerry-Anne; Barter, Philip J; Cochran, Blake J

    2016-02-01

    Human population studies have established that an elevated plasma high-density lipoprotein cholesterol (HDL-C) level is associated with a decreased risk of developing cardiovascular disease. In addition to having several potentially cardioprotective functions, HDLs and apolipoprotein (apo)A-I, the main HDL apolipoprotein, also have antidiabetic properties. Interventions that elevate plasma HDL-C and apoA-I levels improve glycemic control in people with type 2 diabetes mellitus by enhancing pancreatic β-cell function and increasing insulin sensitivity. This review is concerned with recent advances in understanding the mechanisms by which HDLs and apoA-I improve pancreatic β-cell function. HDLs and apoA-I increase insulin synthesis and secretion in pancreatic β cells. The underlying mechanism of this effect is similar to what has been reported for intestinally derived incretins, such as glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide, which both increase β-cell insulin secretion under high glucose conditions. This involves the activation of a heterotrimeric G protein Gαs subunit on the β-cell surface that leads to induction of a transmembrane adenylyl cyclase, increased intracellular cyclic adenosine monophosphate and Ca levels, and activation of protein kinase A. Protein kinase A increases insulin synthesis by excluding FoxO1 from the β-cell nucleus and derepressing transcription of the insulin gene.

  8. Incretins, insulin secretion and Type 2 diabetes mellitus.

    PubMed

    Vilsbøll, T; Holst, J J

    2004-03-01

    When glucose is taken orally, insulin secretion is stimulated much more than it is when glucose is infused intravenously so as to result in similar glucose concentrations. This effect, which is called the incretin effect and is estimated to be responsible for 50 to 70% of the insulin response to glucose, is caused mainly by the two intestinal insulin-stimulating hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Their contributions have been confirmed in mimicry experiments, in experiments with antagonists of their actions, and in experiments where the genes encoding their receptors have been deleted. In patients with Type 2 diabetes, the incretin effect is either greatly impaired or absent, and it is assumed that this could contribute to the inability of these patients to adjust their insulin secretion to their needs. In studies of the mechanism of the impaired incretin effect in Type 2 diabetic patients, it has been found that the secretion of GIP is generally normal, whereas the secretion of GLP-1 is reduced, presumably as a consequence of the diabetic state. It might be of even greater importance that the effect of GLP-1 is preserved whereas the effect of GIP is severely impaired. The impaired GIP effect seems to have a genetic background, but could be aggravated by the diabetic state. The preserved effect of GLP-1 has inspired attempts to treat Type 2 diabetes with GLP-1 or analogues thereof, and intravenous GLP-1 administration has been shown to be able to near-normalize both fasting and postprandial glycaemic concentrations in the patients, perhaps because the treatment compensates for both the impaired secretion of GLP-1 and the impaired action of GIP. Several GLP-1 analogues are currently in clinical development and the reported results are, so far, encouraging.

  9. Effect of tequila on homocysteine, insulin secretion, insulin sensitivity, and metabolic profile in healthy men.

    PubMed

    González-Ortiz, Manuel; Pascoe-González, Sara; Kam-Ramos, Angélica M; Martínez-Abundis, Esperanza

    2005-01-01

    The purpose of this study is to identify the effect of a low dose of tequila on homocysteine, insulin secretion, insulin sensitivity, and metabolic profile in healthy young men. An open clinical trial was carried out in eight healthy nonobese, young male volunteers. The study was divided in two phases. The first one evaluated metabolic changes, including insulin secretion and sensitivity due to acute administration of 30 ml of straight tequila. The second phase of the study evaluated metabolic effects due to the daily administration of 30 ml of tequila during 30 days. There were no significant metabolic changes after the single oral administration of 30 ml of straight tequila. After the administration of tequila during 30 days, a significant increase in homocysteine levels and a tendency to increase the glucose concentration and to decrease the insulin sensitivity were found. Detrimental metabolic changes were observed with the daily administration of 30 ml of tequila during 30 days.

  10. Biomarkers in Fasting Serum to Estimate Glucose Tolerance, Insulin Sensitivity, and Insulin Secretion

    PubMed Central

    Goldfine, Allison B.; Gerwien, Robert W.; Kolberg, Janice A.; O’Shea, Sheila; Hamren, Sarah; Hein, Glenn P.; Xu, Xiaomei M.; Patti, Mary Elizabeth

    2014-01-01

    BACKGROUND Biomarkers for estimating reduced glucose tolerance, insulin sensitivity, or impaired insulin secretion would be clinically useful, since these physiologic measures are important in the pathogenesis of type 2 diabetes mellitus. METHODS We conducted a cross-sectional study in which 94 individuals, of whom 84 had 1 or more risk factors and 10 had no known risk factors for diabetes, underwent oral glucose tolerance testing. We measured 34 protein biomarkers associated with diabetes risk in 250-μL fasting serum samples. We applied multiple regression selection techniques to identify the most informative biomarkers and develop multivariate models to estimate glucose tolerance, insulin sensitivity, and insulin secretion. The ability of the glucose tolerance model to discriminate between diabetic individuals and those with impaired or normal glucose tolerance was evaluated by area under the ROC curve (AUC) analysis. RESULTS Of the at-risk participants, 25 (30%) were found to have impaired glucose tolerance, and 11 (13%) diabetes. Using molecular counting technology, we assessed multiple biomarkers with high accuracy in small volume samples. Multivariate biomarker models derived from fasting samples correlated strongly with 2-h postload glucose tolerance (R2 = 0.45, P < 0.0001), composite insulin sensitivity index (R2 = 0.91, P < 0.0001), and insulin secretion (R2 = 0.45, P < 0.0001). Additionally, the glucose tolerance model provided strong discrimination between diabetes vs impaired or normal glucose tolerance (AUC 0.89) and between diabetes and impaired glucose tolerance vs normal tolerance (AUC 0.78). CONCLUSIONS Biomarkers in fasting blood samples may be useful in estimating glucose tolerance, insulin sensitivity, and insulin secretion. PMID:21149503

  11. ADCY5 Couples Glucose to Insulin Secretion in Human Islets

    PubMed Central

    Mitchell, Ryan K.; Marselli, Lorella; Pullen, Timothy J.; Gimeno Brias, Silvia; Semplici, Francesca; Everett, Katy L.; Cooper, Dermot M.F.; Bugliani, Marco; Marchetti, Piero; Lavallard, Vanessa; Bosco, Domenico; Piemonti, Lorenzo; Johnson, Paul R.; Hughes, Stephen J.; Li, Daliang; Li, Wen-Hong; Shapiro, A.M. James

    2014-01-01

    Single nucleotide polymorphisms (SNPs) within the ADCY5 gene, encoding adenylate cyclase 5, are associated with elevated fasting glucose and increased type 2 diabetes (T2D) risk. Despite this, the mechanisms underlying the effects of these polymorphic variants at the level of pancreatic β-cells remain unclear. Here, we show firstly that ADCY5 mRNA expression in islets is lowered by the possession of risk alleles at rs11708067. Next, we demonstrate that ADCY5 is indispensable for coupling glucose, but not GLP-1, to insulin secretion in human islets. Assessed by in situ imaging of recombinant probes, ADCY5 silencing impaired glucose-induced cAMP increases and blocked glucose metabolism toward ATP at concentrations of the sugar >8 mmol/L. However, calcium transient generation and functional connectivity between individual human β-cells were sharply inhibited at all glucose concentrations tested, implying additional, metabolism-independent roles for ADCY5. In contrast, calcium rises were unaffected in ADCY5-depleted islets exposed to GLP-1. Alterations in β-cell ADCY5 expression and impaired glucose signaling thus provide a likely route through which ADCY5 gene polymorphisms influence fasting glucose levels and T2D risk, while exerting more minor effects on incretin action. PMID:24740569

  12. Direct Stimulation of Islet Insulin Secretion by Glycolytic and Mitochondrial Metabolites in KCl-Depolarized Islets

    PubMed Central

    Deeney, Jude T.; Corkey, Barbara E.

    2016-01-01

    We have previously demonstrated that islet depolarization with 70 mM KCl opens Cx36 hemichannels and allows diffusion of small metabolites and cofactors through the β-cell plasma membrane. We have investigated in this islet “permeabilized” model whether glycolytic and citric acid cycle intermediates stimulate insulin secretion and how it correlates with ATP production (islet content plus extracellular nucleotide accumulation). Glycolytic intermediates (10 mM) stimulated insulin secretion and ATP production similarly. However, they showed differential sensitivities to respiratory chain or enzyme inhibitors. Pyruvate showed a lower secretory capacity and less ATP production than phosphoenolpyruvate, implicating an important role for glycolytic generation of ATP. ATP production by glucose-6-phosphate was not sensitive to a pyruvate kinase inhibitor that effectively suppressed the phosphoenolpyruvate-induced secretory response and islet ATP rise. Strong suppression of both insulin secretion and ATP production induced by glucose-6-phosphate was caused by 10 μM antimycin A, implicating an important role for the glycerophosphate shuttle in transferring reducing equivalents to the mitochondria. Five citric acid cycle intermediates were investigated for their secretory and ATP production capacity (succinate, fumarate, malate, isocitrate and α-ketoglutarate at 5 mM, together with ADP and/or NADP+ to feed the NADPH re-oxidation cycles). The magnitude of the secretory response was very similar among the different mitochondrial metabolites but α-ketoglutarate showed a more sustained second phase of secretion. Gabaculine (1 mM, a GABA-transaminase inhibitor) suppressed the second phase of secretion and the ATP-production stimulated by α-ketoglutarate, supporting a role for the GABA shuttle in the control of glucose-induced insulin secretion. None of the other citric acid intermediates essayed showed any suppression of both insulin secretion or ATP-production by the

  13. Sweet taste receptors regulate basal insulin secretion and contribute to compensatory insulin hypersecretion during the development of diabetes in male mice.

    PubMed

    Kyriazis, George A; Smith, Kathleen R; Tyrberg, Björn; Hussain, Tania; Pratley, Richard E

    2014-06-01

    β-Cells rapidly secrete insulin in response to acute increases in plasma glucose but, upon further continuous exposure to glucose, insulin secretion progressively decreases. Although the mechanisms are unclear, this mode of regulation suggests the presence of a time-dependent glucosensory system that temporarily attenuates insulin secretion. Interestingly, early-stage β-cell dysfunction is often characterized by basal (ie, fasting) insulin hypersecretion, suggesting a disruption of these related mechanisms. Because sweet taste receptors (STRs) on β-cells are implicated in the regulation of insulin secretion and glucose is a bona fide STR ligand, we tested whether STRs mediate this sensory mechanism and participate in the regulation of basal insulin secretion. We used mice lacking STR signaling (T1R2(-/-) knockout) and pharmacologic inhibition of STRs in human islets. Mouse and human islets deprived of STR signaling hypersecrete insulin at short-term fasting glucose concentrations. Accordingly, 5-hour fasted T1R2(-/-) mice have increased plasma insulin and lower glucose. Exposure of isolated wild-type islets to elevated glucose levels reduced STR expression, whereas islets from diabetic (db/db) or diet-induced obese mouse models show similar down-regulation. This transcriptional reprogramming in response to hyperglycemia correlates with reduced STR function in these mouse models, leading to insulin hypersecretion. These findings reveal a novel mechanism by which insulin secretion is physiologically regulated by STRs and also suggest that, during the development of diabetes, STR function is compromised by hyperglycemia leading to hyperinsulinemia. These observations further suggest that STRs might be a promising therapeutic target to prevent and treat type 2 diabetes.

  14. Sweet Taste Receptors Regulate Basal Insulin Secretion and Contribute to Compensatory Insulin Hypersecretion During the Development of Diabetes in Male Mice

    PubMed Central

    Smith, Kathleen R.; Tyrberg, Björn; Hussain, Tania; Pratley, Richard E.

    2014-01-01

    β-Cells rapidly secrete insulin in response to acute increases in plasma glucose but, upon further continuous exposure to glucose, insulin secretion progressively decreases. Although the mechanisms are unclear, this mode of regulation suggests the presence of a time-dependent glucosensory system that temporarily attenuates insulin secretion. Interestingly, early-stage β-cell dysfunction is often characterized by basal (ie, fasting) insulin hypersecretion, suggesting a disruption of these related mechanisms. Because sweet taste receptors (STRs) on β-cells are implicated in the regulation of insulin secretion and glucose is a bona fide STR ligand, we tested whether STRs mediate this sensory mechanism and participate in the regulation of basal insulin secretion. We used mice lacking STR signaling (T1R2−/− knockout) and pharmacologic inhibition of STRs in human islets. Mouse and human islets deprived of STR signaling hypersecrete insulin at short-term fasting glucose concentrations. Accordingly, 5-hour fasted T1R2−/− mice have increased plasma insulin and lower glucose. Exposure of isolated wild-type islets to elevated glucose levels reduced STR expression, whereas islets from diabetic (db/db) or diet-induced obese mouse models show similar down-regulation. This transcriptional reprogramming in response to hyperglycemia correlates with reduced STR function in these mouse models, leading to insulin hypersecretion. These findings reveal a novel mechanism by which insulin secretion is physiologically regulated by STRs and also suggest that, during the development of diabetes, STR function is compromised by hyperglycemia leading to hyperinsulinemia. These observations further suggest that STRs might be a promising therapeutic target to prevent and treat type 2 diabetes. PMID:24712876

  15. Evidence That the Sympathetic Nervous System Elicits Rapid, Coordinated, and Reciprocal Adjustments of Insulin Secretion and Insulin Sensitivity During Cold Exposure.

    PubMed

    Morton, Gregory J; Muta, Kenjiro; Kaiyala, Karl J; Rojas, Jennifer M; Scarlett, Jarrad M; Matsen, Miles E; Nelson, Jarrell T; Acharya, Nikhil K; Piccinini, Francesca; Stefanovski, Darko; Bergman, Richard N; Taborsky, Gerald J; Kahn, Steven E; Schwartz, Michael W

    2017-04-01

    Dynamic adjustment of insulin secretion to compensate for changes of insulin sensitivity that result from alteration of nutritional or metabolic status is a fundamental aspect of glucose homeostasis. To investigate the role of the brain in this coupling process, we used cold exposure as an experimental paradigm because the sympathetic nervous system (SNS) helps to coordinate the major shifts of tissue glucose utilization needed to ensure that increased thermogenic needs are met. We found that glucose-induced insulin secretion declined by 50% in rats housed at 5°C for 28 h, and yet, glucose tolerance did not change, owing to a doubling of insulin sensitivity. These potent effects on insulin secretion and sensitivity were fully reversed by returning animals to room temperature (22°C) for 4 h or by intravenous infusion of the α-adrenergic receptor antagonist phentolamine for only 30 min. By comparison, insulin clearance was not affected by cold exposure or phentolamine infusion. These findings offer direct evidence of a key role for the brain, acting via the SNS, in the rapid, highly coordinated, and reciprocal changes of insulin secretion and insulin sensitivity that preserve glucose homeostasis in the setting of cold exposure.

  16. Insulin secreting and alpha-glucosidase inhibitory activity of hexane extract of Annona squamosa Linn. in streptozotocin (STZ) induced diabetic rats.

    PubMed

    Ranjana; Tripathi, Yamini B

    2014-06-01

    The hexane extract of A. squamosa (ASHE) in 100 and 400 mg/kg body weight dose raised the insulin level when compared with Glimepiride (1 mg/kg) and also inhibited alpha-glucosidase activity when compared with Acarbose (10 mg/kg) in streptozotocin induced diabetic rats. The ASHE significantly reduced peak blood glucose (Gp30) and area under curve (AUC) in diabetic rats in oral glucose (OGTT) and oral sucrose (OSTT) tolerance test, but there was more reduction of Gp30 value than AUC in OSTT. Thus, it can be suggested that the ASHE, has hypoglycemic role at 2 levels, i.e. it acts as secretagogue and also inhibits the intestinal enzymes, responsible for glucose metabolism.

  17. Identification of morin as an agonist of imidazoline I-3 receptor for insulin secretion in diabetic rats.

    PubMed

    Lin, Mang Hung; Hsu, Chia-Chen; Lin, Jenshinn; Cheng, Juei-Tang; Wu, Ming Chang

    2017-07-08

    Morin is a flavonoid contained in guava that is known to reduce hyperglycemia in diabetics. Morin has been demonstrated to increase plasma insulin. However, the mechanism(s) remains unknown. The present study is designed to investigate the effect of morin on the imidazoline receptor (I-R) that regulates insulin secretion. We used Chinese hamster ovary (CHO) cells transfected with an I-R expression construct (NISCH-CHO-K1 cells) to identify the direct effect of morin on the I-R. Moreover, the imidazoline I3 receptor (I-3R) is known to be present in pancreatic β cells and involved in insulin secretion. Therefore, we applied a specific antagonist (KU14R) to block I-3R in diabetic rats. Additionally, the effect of morin on insulin secretion was characterized in isolated pancreatic islets. Morin decreased blood glucose levels by increasing plasma insulin levels in diabetic rats. In CHO cells expressing an I-R, morin increased calcium influx in a dose-dependent manner. Additionally, KU14R dose-dependently inhibited the morin-induced effects, including hypoglycemia and the increase in insulin secretion and plasma C-peptide levels, in diabetic rats. Furthermore, morin enhanced insulin secretion from isolated pancreatic islets, and this effect was also dose-dependently inhibited by KU14R. Phospholipase C (PLC) is known to couple with the I-R, and a PLC inhibitor dose-dependently attenuated the insulin secretion induced by morin in isolated pancreatic islets. Taken together, these data suggest that morin can activate I-3R to enhance insulin secretion. Therefore, it would be useful to develop morin into a treatment for diabetic disorders.

  18. Interleukin-6 Enhances Glucose-Stimulated Insulin Secretion From Pancreatic β-Cells

    PubMed Central

    Suzuki, Toshinobu; Imai, Junta; Yamada, Tetsuya; Ishigaki, Yasushi; Kaneko, Keizo; Uno, Kenji; Hasegawa, Yutaka; Ishihara, Hisamitsu; Oka, Yoshitomo; Katagiri, Hideki

    2011-01-01

    OBJECTIVE Interleukin-6 (IL-6) has a significant impact on glucose metabolism. However, the effects of IL-6 on insulin secretion from pancreatic β-cells are controversial. Therefore, we analyzed IL-6 effects on pancreatic β-cell functions both in vivo and in vitro. RESEARCH DESIGN AND METHODS First, to examine the effects of IL-6 on in vivo insulin secretion, we expressed IL-6 in the livers of mice using the adenoviral gene transfer system. In addition, using both MIN-6 cells, a murine β-cell line, and pancreatic islets isolated from mice, we analyzed the in vitro effects of IL-6 pretreatment on insulin secretion. Furthermore, using pharmacological inhibitors and small interfering RNAs, we studied the intracellular signaling pathway through which IL-6 may affect insulin secretion from MIN-6 cells. RESULTS Hepatic IL-6 expression raised circulating IL-6 and improved glucose tolerance due to enhancement of glucose stimulated-insulin secretion (GSIS). In addition, in both isolated pancreatic islets and MIN-6 cells, 24-h pretreatment with IL-6 significantly enhanced GSIS. Furthermore, pretreatment of MIN-6 cells with phospholipase C (PLC) inhibitors with different mechanisms of action, U-73122 and neomycin, and knockdowns of the IL-6 receptor and PLC-β1, but not with a protein kinase A inhibitor, H-89, inhibited IL-6–induced enhancement of GSIS. An inositol triphosphate (IP3) receptor antagonist, Xestospondin C, also abrogated the GSIS enhancement induced by IL-6. CONCLUSIONS The results obtained from both in vivo and in vitro experiments strongly suggest that IL-6 acts directly on pancreatic β-cells and enhances GSIS. The PLC-IP3–dependent pathway is likely to be involved in IL-6-mediated enhancements of GSIS. PMID:21270264

  19. Melatonin modifies basal and stimulated insulin secretion via NADPH oxidase.

    PubMed

    Simões, Daniel; Riva, Patrícia; Peliciari-Garcia, Rodrigo Antonio; Cruzat, Vinicius Fernandes; Graciano, Maria Fernanda; Munhoz, Ana Claudia; Taneda, Marco; Cipolla-Neto, José; Carpinelli, Angelo Rafael

    2016-12-01

    Melatonin is a hormone synthesized in the pineal gland, which modulates several functions within the organism, including the synchronization of glucose metabolism and glucose-stimulated insulin secretion (GSIS). Melatonin can mediate different signaling pathways in pancreatic islets through two membrane receptors and via antioxidant or pro-oxidant enzymes modulation. NADPH oxidase (NOX) is a pro-oxidant enzyme responsible for the production of the reactive oxygen specie (ROS) superoxide, generated from molecular oxygen. In pancreatic islets, NOX-derived ROS can modulate glucose metabolism and regulate insulin secretion. Considering the roles of both melatonin and NOX in islets, the aim of this study was to evaluate the association of NOX and ROS production on glucose metabolism, basal and GSIS in pinealectomized rats (PINX) and in melatonin-treated isolated pancreatic islets. Our results showed that ROS content derived from NOX activity was increased in PINX at baseline (2.8 mM glucose), which was followed by a reduction in glucose metabolism and basal insulin secretion in this group. Under 16.7 mM glucose, an increase in both glucose metabolism and GSIS was observed in PINX islets, without changes in ROS content. In isolated pancreatic islets from control animals incubated with 2.8 mM glucose, melatonin treatment reduced ROS content, whereas in 16.7 mM glucose, melatonin reduced ROS and GSIS. In conclusion, our results demonstrate that both basal and stimulated insulin secretion can be regulated by melatonin through the maintenance of ROS homeostasis in pancreatic islets. © 2016 Society for Endocrinology.

  20. Ion channels and regulation of insulin secretion in human β-cells

    PubMed Central

    Fridlyand, Leonid E.; Jacobson, David A.; Philipson, L.H.

    2013-01-01

    In mammals an increase in glucose leads to block of ATP dependent potassium channels in pancreatic β cells leading to membrane depolarization. This leads to the repetitive firing of action potentials that increases calcium influx and triggers insulin granule exocytosis. Several important differences between species in this process suggest that a dedicated human-oriented approach is advantageous as extrapolating from rodent data may be misleading in several respects. We examined depolarization-induced spike activity in pancreatic human islet-attached β-cells employing whole-cell patch-clamp methods. We also reviewed the literature concerning regulation of insulin secretion by channel activity and constructed a data-based computer model of human β cell function. The model couples the Hodgkin-Huxley-type ionic equations to the equations describing intracellular Ca2+ homeostasis and insulin release. On the basis of this model we employed computational simulations to better understand the behavior of action potentials, calcium handling and insulin secretion in human β cells under a wide range of experimental conditions. This computational system approach provides a framework to analyze the mechanisms of human β cell insulin secretion. PMID:23624892

  1. Nuclear PLCs affect insulin secretion by targeting PPARγ in pancreatic β cells.

    PubMed

    Fiume, Roberta; Ramazzotti, Giulia; Faenza, Irene; Piazzi, Manuela; Bavelloni, Alberto; Billi, Anna Maria; Cocco, Lucio

    2012-01-01

    Type 2 diabetes is a heterogeneous disorder caused by concomitant impairment of insulin secretion by pancreatic β cells and of insulin action in peripheral target tissues. Studies with inhibitors and agonists established a role for PLC in the regulation of insulin secretion but did not distinguish between effects due to nuclear or cytoplasmic PLC signaling pathways that act in a distinct fashion. We report that in MIN6 β cells, PLCβ1 localized in both nucleus and cytoplasm, PLCδ4 in the nucleus, and PLCγ1 in the cytoplasm. By silencing each isoform, we observed that they all affected glucose-induced insulin release both at basal and high glucose concentrations. To elucidate the molecular basis of PLC regulation, we focused on peroxisome proliferator-activated receptor-γ (PPARγ), a nuclear receptor transcription factor that regulates genes critical to β-cell maintenance and functions. Silencing of PLCβ1 and PLCδ4 resulted in a decrease in the PPARγ mRNA level. By means of a PPARγ-promoter-luciferase assay, the decrease could be attributed to a PLC action on the PPARγ-promoter region. The effect was specifically observed on silencing of the nuclear and not the cytoplasmic PLC. These findings highlight a novel pathway by which nuclear PLCs affect insulin secretion and identify PPARγ as a novel molecular target of nuclear PLCs.

  2. Non-traditional roles of complement in type 2 diabetes: Metabolism, insulin secretion and homeostasis.

    PubMed

    King, Ben C; Blom, Anna M

    2017-04-01

    Type 2 Diabetes (T2D) is a disease of increasing importance and represents a growing burden on global healthcare and human health. In T2D, loss of effectiveness of insulin signaling in peripheral tissues cannot be compensated for by adequate insulin secretion, leading to hyperglycemia and resultant complications. In recent years, inflammation has been identified as a central component of T2D, both in inducing peripheral insulin resistance as well as in the pancreatic islet, where it contributes to loss of insulin secretion and death of insulin-secreting beta cells. In this review we will focus on non-traditional roles of complement proteins which have been identified in T2D-associated inflammation, beta cell secretory function, and in maintaining homeostasis of the pancreatic islet. Improved understanding of both traditional and novel roles of complement proteins in T2D may lead to new therapeutic approaches for this global disease. Copyright © 2016 Elsevier Ltd. All rights reserved.

  3. Hypothalamic prolyl endopeptidase (PREP) regulates pancreatic insulin and glucagon secretion in mice

    PubMed Central

    Kim, Jung Dae; Toda, Chitoku; D’Agostino, Giuseppe; Zeiss, Caroline J.; DiLeone, Ralph J.; Elsworth, John D.; Kibbey, Richard G.; Chan, Owen; Harvey, Brandon K.; Richie, Christopher T.; Savolainen, Mari; Myöhänen, Timo; Jeong, Jin Kwon; Diano, Sabrina

    2014-01-01

    Prolyl endopeptidase (PREP) has been implicated in neuronal functions. Here we report that hypothalamic PREP is predominantly expressed in the ventromedial nucleus (VMH), where it regulates glucose-induced neuronal activation. PREP knockdown mice (Prepgt/gt) exhibited glucose intolerance, decreased fasting insulin, increased fasting glucagon levels, and reduced glucose-induced insulin secretion compared with wild-type controls. Consistent with this, central infusion of a specific PREP inhibitor, S17092, impaired glucose tolerance and decreased insulin levels in wild-type mice. Arguing further for a central mode of action of PREP, isolated pancreatic islets showed no difference in glucose-induced insulin release between Prepgt/gt and wild-type mice. Furthermore, hyperinsulinemic euglycemic clamp studies showed no difference between Prepgt/gt and wild-type control mice. Central PREP regulation of insulin and glucagon secretion appears to be mediated by the autonomic nervous system because Prepgt/gt mice have elevated sympathetic outflow and norepinephrine levels in the pancreas, and propranolol treatment reversed glucose intolerance in these mice. Finally, re-expression of PREP by bilateral VMH injection of adeno-associated virus–PREP reversed the glucose-intolerant phenotype of the Prepgt/gt mice. Taken together, our results unmask a previously unknown player in central regulation of glucose metabolism and pancreatic function. PMID:25071172

  4. Insight into Insulin Secretion from Transcriptome and Genetic Analysis of Insulin-Producing Cells of Drosophila

    PubMed Central

    Cao, Jian; Ni, Julie; Ma, Wenxiu; Shiu, Vanessa; Milla, Luis A.; Park, Sangbin; Spletter, Maria L.; Tang, Sheng; Zhang, Jun; Wei, Xing; Kim, Seung K.; Scott, Matthew P.

    2014-01-01

    Insulin-producing cells (IPCs) in the Drosophila brain produce and release insulin-like peptides (ILPs) to the hemolymph. ILPs are crucial for growth and regulation of metabolic activity in flies, functions analogous to those of mammalian insulin and insulin-like growth factors (IGFs). To identify components functioning in IPCs to control ILP production, we employed genomic and candidate gene approaches. We used laser microdissection and messenger RNA sequencing to characterize the transcriptome of larval IPCs. IPCs highly express many genes homologous to genes active in insulin-producing β-cells of the mammalian pancreas. The genes in common encode ILPs and proteins that control insulin metabolism, storage, secretion, β-cell proliferation, and some not previously linked to insulin production or β-cell function. Among these novelties is unc-104, a kinesin 3 family gene, which is more highly expressed in IPCs compared to most other neurons. Knockdown of unc-104 in IPCs impaired ILP secretion and reduced peripheral insulin signaling. Unc-104 appears to transport ILPs along axons. As a complementary approach, we tested dominant-negative Rab genes to find Rab proteins required in IPCs for ILP production or secretion. Rab1 was identified as crucial for ILP trafficking in IPCs. Inhibition of Rab1 in IPCs increased circulating sugar levels, delayed development, and lowered weight and body size. Immunofluorescence labeling of Rab1 showed its tight association with ILP2 in the Golgi of IPCs. Unc-104 and Rab1 join other proteins required for ILP transport in IPCs. PMID:24558258

  5. Assessment of the Role of Metabolic Determinants on the Relationship between Insulin Sensitivity and Secretion

    PubMed Central

    Galgani, Jose E.; Gómez, Carmen; Mizgier, Maria L.; Gutierrez, Juan; Santos, Jose L.; Olmos, Pablo; Mari, Andrea

    2016-01-01

    Background Insulin secretion correlates inversely with insulin sensitivity, which may suggest the existence of a crosstalk between peripheral organs and pancreas. Such interaction might be mediated through glucose oxidation that may drive the release of circulating factors with action on insulin secretion. Aim To evaluate the association between whole-body carbohydrate oxidation and circulating factors with insulin secretion to consecutive oral glucose loading in non-diabetic individuals. Methods Carbohydrate oxidation was measured after an overnight fast and for 6 hours after two 3-h apart 75-g oral glucose tolerance tests (OGTT) in 53 participants (24/29 males/females; 34±9 y; 27±4 kg/m2). Insulin secretion was estimated by deconvolution of serum C-peptide concentration, β cell function by mathematical modelling and insulin sensitivity from an OGTT. Circulating lactate, free-fatty acids (FFA) and candidate chemokines were assessed before and after OGTT. The effect of recombinant RANTES (regulated on activation, normal T cell expressed and secreted) and IL8 (interleukin 8) on insulin secretion from isolated mice islets was also measured. Results Carbohydrate oxidation assessed over the 6-h period did not relate with insulin secretion (r = -0.11; p = 0.45) or β cell function indexes. Circulating lactate and FFA showed no association with 6-h insulin secretion. Circulating chemokines concentration increased upon oral glucose stimulation. Insulin secretion associated with plasma IL6 (r = 0.35; p<0.05), RANTES (r = 0.30; p<0.05) and IL8 (r = 0.41; p<0.05) determined at 60 min OGTT. IL8 was independently associated with in vivo insulin secretion; however, it did not affect in vitro insulin secretion. Conclusion Whole-body carbohydrate oxidation appears to have no influence on insulin secretion or putative circulating mediators. IL8 may be a potential factor influencing insulin secretion. PMID:28002466

  6. Assessment of the Role of Metabolic Determinants on the Relationship between Insulin Sensitivity and Secretion.

    PubMed

    Galgani, Jose E; Gómez, Carmen; Mizgier, Maria L; Gutierrez, Juan; Santos, Jose L; Olmos, Pablo; Mari, Andrea

    2016-01-01

    Insulin secretion correlates inversely with insulin sensitivity, which may suggest the existence of a crosstalk between peripheral organs and pancreas. Such interaction might be mediated through glucose oxidation that may drive the release of circulating factors with action on insulin secretion. To evaluate the association between whole-body carbohydrate oxidation and circulating factors with insulin secretion to consecutive oral glucose loading in non-diabetic individuals. Carbohydrate oxidation was measured after an overnight fast and for 6 hours after two 3-h apart 75-g oral glucose tolerance tests (OGTT) in 53 participants (24/29 males/females; 34±9 y; 27±4 kg/m2). Insulin secretion was estimated by deconvolution of serum C-peptide concentration, β cell function by mathematical modelling and insulin sensitivity from an OGTT. Circulating lactate, free-fatty acids (FFA) and candidate chemokines were assessed before and after OGTT. The effect of recombinant RANTES (regulated on activation, normal T cell expressed and secreted) and IL8 (interleukin 8) on insulin secretion from isolated mice islets was also measured. Carbohydrate oxidation assessed over the 6-h period did not relate with insulin secretion (r = -0.11; p = 0.45) or β cell function indexes. Circulating lactate and FFA showed no association with 6-h insulin secretion. Circulating chemokines concentration increased upon oral glucose stimulation. Insulin secretion associated with plasma IL6 (r = 0.35; p<0.05), RANTES (r = 0.30; p<0.05) and IL8 (r = 0.41; p<0.05) determined at 60 min OGTT. IL8 was independently associated with in vivo insulin secretion; however, it did not affect in vitro insulin secretion. Whole-body carbohydrate oxidation appears to have no influence on insulin secretion or putative circulating mediators. IL8 may be a potential factor influencing insulin secretion.

  7. The Possible Mechanisms of the Impaired Insulin Secretion in Hypothyroid Rats.

    PubMed

    Godini, Aliashraf; Ghasemi, Asghar; Zahediasl, Saleh

    2015-01-01

    Although the insulin secretion deficit in hypothyroid male rats has been documented, the underling mechanisms of the effect of hypothyroidism on insulin secretion are not clear. Isolated islets of the PTU-induced hypothyroid and control rats were exposed to glibenclamide, acetylcholine, and nifedipine in the presence of glucose concentrations of 2.8 or 8.3 and 16.7 mmol/L. Glucokinase and hexokinase specific activity, glucokinase content, and glucose transporter 2 protein expression were also determined in the isolated islets. Isolated islets from the hypothyroid rats showed a defect in insulin secretion in response to high glucose. In the presence of glibenclamide or acetylcholine, the isolated islets from the hypothyroid and control rats stimulated by glucose concentration of 16.7 mmol/L secreted similar amounts of insulin. In the presence of glucose concentrations of 8.3 mmol/L and 16.7 mmol/L, nifedipine was able to diminish insulin secretion from isolated islets of both groups, indicating that probably the defect may not arise from L type calcium channels or the steps beyond depolarization or the elements involved in the acetylcoline signaling pathway. Glucokinase content and hexokinase specific activity were also the same in the control and hypothyroid groups. On the other hand, glucokinase specific activity and glucose transporter 2 protein expression were significantly (p<0.001 and p<0.01 respectively) lower in the islets isolated from the hypothyroid rats (6.50 ± 0.46 mU/min/mg protein and 0.55 ± 0.09 arbitrary unit) compared to the controls (10.93 ± 0.83 mU/min/mg protein and 0.98 ± 0.07 arbitrary unit) respectively. In conclusion, the results of this study indicated that hypothyroidism reduced insulin secretion from isolated pancreatic islets, which confirms the finding of the previous studies; in addition, the insulin secretion deficit observed in hypothyroid rats may arise from the abnormalities in some parts of the glucose sensor apparatus of the

  8. Effect of ovarian suppression with gonadotropin-releasing hormone agonist on glucose disposal and insulin secretion.

    PubMed

    Toth, Michael J; Cooper, Brian C; Pratley, Richard E; Mari, Andrea; Matthews, Dwight E; Casson, Peter R

    2008-06-01

    Several lines of evidence suggest that ovarian hormones influence glucose homeostasis, although their exact role in humans has not been clearly defined. In the present study, we sought to test the hypothesis that ovarian hormones regulate glucose homeostasis by examining the effect of pharmacologically induced ovarian hormone deficiency on glucose disposal and insulin secretion. Young, healthy women with regular menstrual patterns were studied during the follicular and luteal phases of their cycle at baseline and after 2 mo of treatment with gonadotropin-releasing hormone agonist (GnRHa; n = 7) or placebo (n = 6). Using hyperglycemic clamps, in combination with stable isotope-labeled (i.e., (13)C and (2)H) glucose tracers, we measured glucose disposal and insulin secretion. Additionally, we assessed body composition and regional fat distribution using radiologic imaging techniques as well as glucoregulatory hormones. Ovarian hormone suppression with GnRHa did not alter body composition, abdominal fat distribution, or thigh tissue composition. There was no effect of ovarian suppression on total, oxidative, or nonoxidative glucose disposal expressed relative to plasma insulin level. Similarly, no effect of ovarian hormone deficiency was observed on first- or second-phase insulin secretion or insulin clearance. Finally, ovarian hormone deficiency was associated with an increase in circulating adiponectin levels but no change in leptin concentration. Our findings suggest that a brief period of ovarian hormone deficiency in young, healthy, eugonadal women does not alter glucose disposal index or insulin secretion, supporting the conclusion that ovarian hormones play a minimal role in regulating glucose homeostasis. Our data do, however, support a role for ovarian hormones in the regulation of plasma adiponectin levels.

  9. Upregulated insulin secretion in insulin-resistant mice: evidence of increased islet GLP1 receptor levels and GPR119-activated GLP1 secretion.

    PubMed

    Ahlkvist, L; Brown, K; Ahrén, B

    2013-06-01

    We previously demonstrated that the overall incretin effect and the β-cell responsiveness to glucagon-like peptide-1 (GLP1) are increased in insulin-resistant mice and may contribute to the upregulated β-cell function. Now we examined whether this could, first, be explained by increased islet GLP1 receptor (GLP1R) protein levels and, secondly, be leveraged by G-protein-coupled receptor 119 (GPR119) activation, which stimulates GLP1 secretion. Female C57BL/6J mice, fed a control (CD, 10% fat) or high-fat (HFD, 60% fat) diet for 8 weeks, were anesthetized and orally given a GPR119 receptor agonist (GSK706A; 10 mg/kg) or vehicle, followed after 10 min with gavage with a liquid mixed meal (0.285 kcal). Blood was sampled for determination of glucose, insulin, intact GLP1, and glucagon, and islets were isolated for studies on insulin and glucagon secretion and GLP1R protein levels. In HFD vs CD mice, GPR119 activation augmented the meal-induced increase in the release of both GLP1 (AUCGLP1 81±9.6 vs 37±6.9 pM×min, P=0.002) and insulin (AUCINS 253±29 vs 112±19 nM×min, P<0.001). GPR119 activation also significantly increased glucagon levels in both groups (P<0.01) with, however, no difference between the groups. By contrast, GPR119 activation did not affect islet hormone secretion from isolated islets. Glucose elimination after meal ingestion was significantly increased by GPR119 activation in HFD mice (0.57±0.04 vs 0.43±0.03% per min, P=0.014) but not in control mice. Islet GLP1R protein levels was higher in HFD vs CD mice (0.8±0.1 vs 0.5±0.1, P=0.035). In conclusion, insulin-resistant mice display increased islet GLP1R protein levels and augmented meal-induced GLP1 and insulin responses to GPR119 activation, which results in increased glucose elimination. We suggest that the increased islet GLP1R protein levels together with the increased GLP1 release may contribute to the upregulated β-cell function in insulin resistance.

  10. Inhibition of connexin 36 hemichannels by glucose contributes to the stimulation of insulin secretion.

    PubMed

    Pizarro-Delgado, Javier; Fasciani, Ilaria; Temperan, Ana; Romero, María; González-Nieto, Daniel; Alonso-Magdalena, Paloma; Nualart-Marti, Anna; Estil'les, Elisabet; Paul, David L; Martín-del-Río, Rafael; Montanya, Eduard; Solsona, Carles; Nadal, Angel; Barrio, Luis Carlos; Tamarit-Rodríguez, J

    2014-06-15

    The existence of functional connexin36 (Cx36) hemichannels in β-cells was investigated in pancreatic islets of rat and wild-type (Cx36(+/+)), monoallelic (Cx36(+/-)), and biallelic (Cx36(-/-)) knockout mice. Hemichannel opening by KCl depolarization was studied by measuring ATP release and changes of intracellular ATP (ADP). Cx36(+/+) islets lost ATP after depolarization with 70 mM KCl at 5 mM glucose; ATP loss was prevented by 8 and 20 mM glucose or 50 μM mefloquine (connexin inhibitor). ATP content was higher in Cx36(-/-) than Cx36(+/+) islets and was not decreased by KCl depolarization; Cx36(+/-) islets showed values between that of control and homozygous islets. Five minimolar extracellular ATP increased ATP content and ATP/ADP ratio and induced a biphasic insulin secretion in depolarized Cx36(+/+) and Cx36(+/-) but not Cx36(-/-) islets. Cx36 hemichannels expressed in oocytes opened upon depolarization of membrane potential, and their activation was inhibited by mefloquine and glucose (IC₅₀ ∼8 mM). It is postulated that glucose-induced inhibition of Cx36 hemichannels in islet β-cells might avoid depolarization-induced ATP loss, allowing an optimum increase of the ATP/ADP ratio by sugar metabolism and a biphasic stimulation of insulin secretion. Gradual suppression of glucose-induced insulin release in Cx36(+/-) and Cx36(-/-) islets confirms that Cx36 gap junction channels are necessary for a full secretory stimulation and might account for the glucose intolerance observed in mice with defective Cx36 expression. Mefloquine targeting of Cx36 on both gap junctions and hemichannels also suppresses glucose-stimulated secretion. By contrast, glucose stimulation of insulin secretion requires Cx36 hemichannels' closure but keeping gap junction channels opened.

  11. PRMT4 is involved in insulin secretion via the methylation of histone H3 in pancreatic β cells.

    PubMed

    Kim, Joong Kwan; Lim, Yongchul; Lee, Jung Ok; Lee, Young-Sun; Won, Nam Hee; Kim, Hyun; Kim, Hyeon Soo

    2015-06-01

    The relationship between protein arginine methyltransferases (PRMTs) and insulin synthesis in β cells is not yet well understood. In the present study, we showed that PRMT4 expression was increased in INS-1 and HIT-T15 pancreatic β cells under high-glucose conditions. In addition, asymmetric dimethylation of Arg17 in histone H3 was significantly increased in both cell lines in the presence of glucose. The inhibition or knockdown of PRMT4 suppressed glucose-induced insulin gene expression in INS-1 cells by 81.6 and 79% respectively. Additionally, the overexpression of mutant PRMT4 also significantly repressed insulin gene expression. Consistently, insulin secretion induced in response to high levels of glucose was decreased by both PRMT4 inhibition and knockdown. Moreover, the inhibition of PRMT4 blocked high-glucose-induced insulin gene expression and insulin secretion in primary pancreatic islets. These results indicate that PRMT4 might be a key regulator of high-glucose-induced insulin secretion from pancreatic β cells via H3R17 methylation.

  12. Effect of Gymnema sylvestre Administration on Metabolic Syndrome, Insulin Sensitivity, and Insulin Secretion.

    PubMed

    Zuñiga, Laura Y; González-Ortiz, Manuel; Martínez-Abundis, Esperanza

    2017-08-01

    Gymnema sylvestre is a medicinal plant whose consumption has demonstrated benefits on lipid and glucose levels, blood pressure, and body weight (BWt). The aim of this study was to evaluate the effect of G. sylvestre administration on metabolic syndrome (MetS), insulin secretion, and insulin sensitivity. A randomized, double-blind, placebo-controlled clinical trial was carried out in 24 patients (without pharmacological treatment), 30-60 years old, with diagnosis of MetS in accordance with the modified International Diabetes Federation criteria. Patients were randomly assigned to receive G. sylvestre or placebo twice daily before breakfast and dinner in 300 mg capsules for a total of 600 mg per day for 12 weeks. Before and after the intervention, the components of MetS were evaluated as well as BWt, body mass index (BMI), total cholesterol, low-density lipoprotein cholesterol, and very low-density lipoprotein (VLDL). Area under the curve of glucose and insulin, phases of insulin secretion, and insulin sensitivity were calculated. Statistical analysis was performed using Wilcoxon signed-rank, Mann-Whitney U, and chi-square tests; P ≤ .05 was considered statistically significant. After G. sylvestre administration, significant decreases in BWt (81.3 ± 10.6 kg vs. 77.9 ± 8.4 kg, P = .02), BMI (31.2 ± 2.5 kg/m(2) vs. 30.4 ± 2.2 kg/m(2), P = .02), and VLDL levels (0.45 ± 0.15 mmol/dL vs. 0.35 ± 0.15 mmol/dL, P = .05) were observed, without modifying the components of MetS, insulin secretion, and insulin sensitivity. In conclusion, G. sylvestre administration decreased BWt, BMI, and VLDL levels in subjects with MetS, without changes in insulin secretion and insulin sensitivity.

  13. Dietary Sodium Restriction Decreases Insulin Secretion Without Affecting Insulin Sensitivity in Humans

    PubMed Central

    Byrne, Loretta M.; Yu, Chang; Wang, Thomas J.; Brown, Nancy J.

    2014-01-01

    Context: Interruption of the renin-angiotensin-aldosterone system prevents incident diabetes in high-risk individuals, although the mechanism remains unclear. Objective: To test the hypothesis that activation of the endogenous renin-angiotensin-aldosterone system or exogenous aldosterone impairs insulin secretion in humans. Design: We conducted a randomized, blinded crossover study of aldosterone vs vehicle and compared the effects of a low-sodium versus a high-sodium diet. Setting: Academic clinical research center. Participants: Healthy, nondiabetic, normotensive volunteers. Interventions: Infusion of exogenous aldosterone (0.7 μg/kg/h for 12.5 h) or vehicle during low or high sodium intake. Low sodium (20 mmol/d; n = 12) vs high sodium (160 mmol/d; n = 17) intake for 5–7 days. Main Outcome Measures: Change in acute insulin secretory response assessed during hyperglycemic clamps while in sodium balance during a low-sodium vs high-sodium diet during aldosterone vs vehicle. Results: A low-sodium diet increased endogenous aldosterone and plasma renin activity, and acute glucose-stimulated insulin (−16.0 ± 5.6%; P = .007) and C-peptide responses (−21.8 ± 8.4%; P = .014) were decreased, whereas the insulin sensitivity index was unchanged (−1.0 ± 10.7%; P = .98). Aldosterone infusion did not affect the acute insulin response (+1.8 ± 4.8%; P = .72) or insulin sensitivity index (+2.0 ± 8.8%; P = .78). Systolic blood pressure and serum potassium were similar during low and high sodium intake and during aldosterone infusion. Conclusions: Low dietary sodium intake reduces insulin secretion in humans, independent of insulin sensitivity. PMID:25029426

  14. Racial (black-white) differences in insulin secretion and clearance in adolescents: the Bogalusa heart study.

    PubMed

    Jiang, X; Srinivasan, S R; Radhakrishnamurthy, B; Dalferes, E R; Berenson, G S

    1996-03-01

    Earlier we found black-white contrast in insulin levels in adolescents. The purpose of this study is to assess whether this difference is attributable to alterations in insulin secretion and/or clearance. Fasting circulating insulin and C-peptide concentrations were examined in 1157 adolescents aged 11 to 18 years from a biracial community. Fasting plasma C-peptide, C-peptide to insulin ratio, and glucose to insulin ratio were used as indices of insulin secretion, hepatic insulin clearance, and insulin sensitivity, respectively. After adjusting several covariates (age, sexual maturation, and obesity), black adolescents had higher insulin levels (14.99 vs 12.66 microU/mL in girls). However, they had lower C-peptide levels than their white counterparts, indicating lower insulin secretion by pancreatic beta cells in black adolescents. Moreover, black adolescents had lower levels of C-peptide to insulin ratio than white adolescents (0.14 vs 0.17), suggesting reduced hepatic insulin clearance in black adolescents. In addition, significantly lower levels of glucose to insulin ratio in black girls suggest a reduced insulin sensitivity in this group. Further, differences in insulin levels between white and black girls disappeared after adjusting for differences in C-peptide to insulin ratio. These data suggest that elevated insulin levels observed in black adolescents, especially in black girls, may be attributed to their decreased hepatic insulin clearance, not hypersecretion of insulin.

  15. Glucagon regulates hepatic kisspeptin to impair insulin secretion.

    PubMed

    Song, Woo-Jin; Mondal, Prosenjit; Wolfe, Andrew; Alonso, Laura C; Stamateris, Rachel; Ong, Benny W T; Lim, Owen C; Yang, Kil S; Radovick, Sally; Novaira, Horacio J; Farber, Emily A; Farber, Charles R; Turner, Stephen D; Hussain, Mehboob A

    2014-04-01

    Early in the pathogenesis of type 2 diabetes mellitus (T2DM), dysregulated glucagon secretion from pancreatic α cells occurs prior to impaired glucose-stimulated insulin secretion (GSIS) from β cells. However, whether hyperglucagonemia is causally linked to β cell dysfunction remains unclear. Here we show that glucagon stimulates via cAMP-PKA-CREB signaling hepatic production of the neuropeptide kisspeptin1, which acts on β cells to suppress GSIS. Synthetic kisspeptin suppresses GSIS in vivo in mice and from isolated islets in a kisspeptin1 receptor-dependent manner. Kisspeptin1 is increased in livers and in serum from humans with T2DM and from mouse models of diabetes mellitus. Importantly, liver Kiss1 knockdown in hyperglucagonemic, glucose-intolerant, high-fat-diet fed, and Lepr(db/db) mice augments GSIS and improves glucose tolerance. These observations indicate a hormonal circuit between the liver and the endocrine pancreas in glycemia regulation and suggest in T2DM a sequential link between hyperglucagonemia via hepatic kisspeptin1 to impaired insulin secretion.

  16. Increased expression of the diabetes gene SOX4 reduces insulin secretion by impaired fusion pore expansion

    PubMed Central

    Collins, Stephan C.; Do, Hyun Woong; Hastoy, Benoit; Hugill, Alison; Adam, Julie; Chibalina, Margarita V.; Galvanovskis, Juris; Godazgar, Mahdieh; Lee, Sheena; Goldsworthy, Michelle; Salehi, Albert; Tarasov, Andrei I.; Rosengren, Anders H.; Cox, Roger; Rorsman, Patrik

    2016-01-01

    The transcription factor Sox4 has been proposed to underlie the increased type-2 diabetes risk linked to an intronic SNP in CDKAL1. In a mouse model expressing a mutant form of Sox4, glucose-induced insulin secretion is reduced by 40% despite normal intracellular Ca2+ signalling and depolarization-evoked exocytosis. This paradox is explained by a 4-fold increase in kiss-and-run exocytosis (as determined by single-granule exocytosis measurements), in which the fusion pore connecting the granule lumen to the exterior only expands to a diameter of 2 nm that does not allow the exit of insulin. Microarray analysis indicated that this correlated with an increased expression of the exocytosis-regulating protein Stxbp6. In a large collection of human islet preparations (n=63), STXBP6 expression and GIIS correlated positively and negatively with SOX4 expression, respectively. Overexpression of SOX4 in the human insulin-secreting cell EndoC-βH2 interfered with granule emptying and inhibited hormone release, the latter effect was reversed by silencing of STXBP6. These data suggest that increased SOX4 expression inhibits insulin secretion and increased diabetes risk by upregulation of STXBP6 and an increase in kiss-and-run exocytosis at the expense of full fusion. We propose that pharmacological interventions promoting fusion pore expansion may be effective in diabetes therapy. PMID:26993066

  17. Palmitic acid acutely inhibits acetylcholine- but not GLP-1-stimulated insulin secretion in mouse pancreatic islets

    PubMed Central

    Qin, Wei; Vinogradov, Sergei A.; Wilson, David F.; Matschinsky, Franz M.

    2010-01-01

    Fatty acids, acetylcholine, and GLP-1 enhance insulin secretion in a glucose-dependent manner. However, the interplay between glucose, fatty acids, and the neuroendocrine regulators of insulin secretion is not well understood. Therefore, we studied the acute effects of PA (alone or in combination with glucose, acetylcholine, or GLP-1) on isolated cultured mouse islets. Two different sets of experiments were designed. In one, a fixed concentration of 0.5 mM of PA bound to 0.15 mM BSA was used; in the other, a PA ramp from 0 to 0.5 mM was applied at a fixed albumin concentration of 0.15 mM so that the molar PA/BSA ratio changed within the physiological range. At a fixed concentration of 0.5 mM, PA markedly inhibited acetylcholine-stimulated insulin release, the rise of intracellular Ca2+, and enhancement of cAMP production but did not influence the effects of GLP-1 on these parameters of islet cell function. 2-ADB, an IP3 receptor inhibitor, reduced the effect of acetylcholine on insulin secretion and reversed the effect of PA on acetylcholine-stimulated insulin release. Islet perfusion for 35–40 min with 0.5 mM PA significantly reduced the calcium storage capacity of ER measured by the thapsigargin-induced Ca2+ release. Oxygen consumption due to low but not high glucose was reduced by PA. When a PA ramp from 0 to 0.5 mM was applied in the presence of 8 mM glucose, PA at concentrations as low as 50 μM significantly augmented glucose-stimulated insulin release and markedly reduced acetylcholine's effects on hormone secretion. We thus demonstrate that PA acutely reduces the total oxygen consumption response to glucose, glucose-dependent acetylcholine stimulation of insulin release, Ca2+, and cAMP metabolism, whereas GLP-1's actions on these parameters remain unaffected or potentiated. We speculate that acute emptying of the ER calcium by PA results in decreased glucose stimulation of respiration and acetylcholine potentiation of insulin secretion. PMID:20606076

  18. Sox17 Regulates Insulin Secretion in the Normal and Pathologic Mouse β Cell

    PubMed Central

    Jonatan, Diva; Spence, Jason R.; Method, Anna M.; Kofron, Matthew; Sinagoga, Katie; Haataja, Leena; Arvan, Peter; Deutsch, Gail H.; Wells, James M.

    2014-01-01

    SOX17 is a key transcriptional regulator that can act by regulating other transcription factors including HNF1β and FOXA2, which are known to regulate postnatal β cell function. Given this, we investigated the role of SOX17 in the developing and postnatal pancreas and found a novel role for SOX17 in regulating insulin secretion. Deletion of the Sox17 gene in the pancreas (Sox17-paLOF) had no observable impact on pancreas development. However, Sox17-paLOF mice had higher islet proinsulin protein content, abnormal trafficking of proinsulin, and dilated secretory organelles suggesting that Sox17-paLOF adult mice are prediabetic. Consistant with this, Sox17-paLOF mice were more susceptible to aged-related and high fat diet-induced hyperglycemia and diabetes. Overexpression of Sox17 in mature β cells using Ins2-rtTA driver mice resulted in precocious secretion of proinsulin. Transcriptionally, SOX17 appears to broadly regulate secretory networks since a 24-hour pulse of SOX17 expression resulted in global transcriptional changes in factors that regulate hormone transport and secretion. Lastly, transient SOX17 overexpression was able to reverse the insulin secretory defects observed in MODY4 animals and restored euglycemia. Together, these data demonstrate a critical new role for SOX17 in regulating insulin trafficking and secretion and that modulation of Sox17-regulated pathways might be used therapeutically to improve cell function in the context of diabetes. PMID:25144761

  19. α 1-antitrypsin enhances insulin secretion and prevents cytokine-mediated apoptosis in pancreatic β-cells.

    PubMed

    Kalis, Martins; Kumar, Rajesh; Janciauskiene, Sabina; Salehi, Albert; Cilio, Corrado M

    2010-01-01

    α1-antitrypsin (AAT) is a serine protease inhibitor, which recently has been shown to prevent type 1 diabetes (T1D) development, to prolong islet allograft survival and to inhibit β-cell apoptosis in vivo. It has also been reported that T1D patients have significantly lower plasma concentrations of AAT suggesting the potential role of AAT in the pathogenesis of T1D. We have investigated whether plasma-purified AAT can affect β-cell function in vitro. INS-1E cells or primary rat pancreatic islets were used to study the effect of AAT on insulin secretion after glucose, glucagon-like peptide-1 (GLP-1) and forskolin stimulation and on cytokine-mediated apoptosis. The secreted insulin and total cyclic AMP (cAMP) were determined using radioimmunoassay and apoptosis was evaluated by propidium iodide staining followed by FACS analysis. We found that AAT increases insulin secretion in a glucose-dependent manner, potentiates the effect of GLP-1 and forskolin and neutralizes the inhibitory effect of clonidine on insulin secretion. The effect of AAT on insulin secretion was accompanied by an increase in cAMP levels. In addition, AAT protected INS-1E cells from cytokine-induced apoptosis. Our findings show that AAT stimulates insulin secretion and protects β-cells against cytokine-induced apoptosis, and these effects of AAT seem to be mediated through the cAMP pathway. In view of these novel findings we suggest that AAT may represent a novel anti-inflammatory compound to protect β-cells under the immunological attack in T1D but also therapeutic strategy to potentiate insulin secretion in type 2 diabetes (T2D).

  20. Direct glucocorticoid inhibition of insulin secretion. An in vitro study of dexamethasone effects in mouse islets.

    PubMed Central

    Lambillotte, C; Gilon, P; Henquin, J C

    1997-01-01

    The direct effects of glucocorticoids on pancreatic beta cell function were studied with normal mouse islets. Dexamethasone inhibited insulin secretion from cultured islets in a concentration-dependent manner: maximum of approximately 75% at 250 nM and IC50 at approximately 20 nM dexamethasone. This inhibition was of slow onset (0, 20, and 40% after 1, 2, and 3 h) and only slowly reversible. It was prevented by a blocker of nuclear glucocorticoid receptors, by pertussis toxin, by a phorbol ester, and by dibutyryl cAMP, but was unaffected by an increase in the fuel content of the culture medium. Dexamethasone treatment did not affect islet cAMP levels but slightly reduced inositol phosphate formation. After 18 h of culture with or without 1 microM dexamethasone, the islets were perifused and stimulated by a rise in the glucose concentration from 3 to 15 mM. Both phases of insulin secretion were similarly decreased in dexamethasone-treated islets as compared with control islets. This inhibition could not be ascribed to a lowering of insulin stores (higher in dexamethasone-treated islets), to an alteration of glucose metabolism (glucose oxidation and NAD(P)H changes were unaffected), or to a lesser rise of cytoplasmic Ca2+ in beta cells (only the frequency of the oscillations was modified). Dexamethasone also inhibited insulin secretion induced by arginine, tolbutamide, or high K+. In this case also the inhibition was observed despite a normal rise of cytoplasmic Ca2+. In conclusion, dexamethasone inhibits insulin secretion through a genomic action in beta cells that leads to a decrease in the efficacy of cytoplasmic Ca2+ on the exocytotic process. PMID:9022074

  1. Insulin and growth hormone secretion in the nephrotic syndrome.

    PubMed

    Bridgman, J F; Summerskill, J; Buckler, J M; Hellman, B; Rosen, S M

    1975-01-01

    Carbohydrate metabolism was studied in a series of patients with the nephrotic syndrome and compared with a similar number of normal controls. The nephrotic syndrome was associated with a smaller secretion of insulin in response to intravenous glucose and tolbutamide than occurred in normals. In the syndrom fasting serum growth hormone (G.H.) concentrations were increased and did not show the characteristic suppression after glucose administration, and the disappearance rate of glucose (k value) was lower. well marked correlation existed between serum G.H. concentrations and the total urinary protein excreted. These abnormal findings returned to normal in a patient who underwent a repeat study when the nephrotic syndrome had resolved.

  2. The insulin secretion of a minced neonatal rat pancreas cultured in a pancreatic chamber, in response to various insulin secretagogues.

    PubMed

    Araki, Y; Yoshioka, K; Inoue, Y; Nakamura, Y; Nakamura, N; Nakano, K; Yoshida, T; Kondo, M

    1981-02-01

    The minced pancreas of the neonatal rat was cultured for 35 days in a pancreatic chamber which was constructed of a plastic tube and an ultrafiltration membrane. Insulin and amylase secreted from this pancreatic chamber into the culture medium were measured. During the experiment, the concentration of glucose in the culture medium was changed between 5.5 and 16.5 mM at 2-3 day intervals in order to determine the insulin secretory response of the pancreatic tissue. Insulin secretion was markedly increased in response to 16.5 mM glucose. The ratio of insulin secretion to amylase secretion in the culture medium increased with the advance of culture days although secretions of both insulin and amylase decreased individually. On the 7th culture day, short term incubations were performed to test with various insulin secretagogues; obvious insulin release into the incubation medium was observed. These results show that the pancreatic chamber also in vitro secretes insulin rapidly and significantly in response to various stimuli; that by longer culture of a neonatal rat pancreas in this device, insulin secretory cells without exocrine tissue would be obtained without using digestive enzymes; that application of a pancreatic chamber for a pancreatic transplantation may be feasible.

  3. Engineering of pseudoislets: effect on insulin secretion activity by cell number, cell population, and microchannel networks.

    PubMed

    Kojima, N; Takeuchi, S; Sakai, Y

    2014-05-01

    Engineered pseudoislets reconstituted from a suspension of pancreatic α and β cells have the potential to relieve the shortage of donor islets for transplantation in the treatment of type 1 diabetes. However, the methods to fabricate pseudoislets are not well developed. In this study, we attempted to generate pseudoislets, which show a higher potential for glucose-induced insulin secretion, by altering total cell number, adjusting the cell ratio of pancreatic α and β cells, and fabricating microchannel networks with the use of alginate hydrogel beads. To effectively aggregate α and β cells and hydrogel beads, we used a previously established rapid aggregation method. When pseudoislets were reconstituted with 8,000 cells in a 1:8 α/β-cell ratio, we observed that the glucose-induced insulin secretion was enhanced by 3.1 times compared with the pseudoislets formed with β cells only. In addition, embedding of microchannel networks increased the insulin secretion rate by 4.4 times compared with the pseudoislets without the microstructures. These findings demonstrated that active modification was effective in reconstituting higher functional pseudoislets, which may be useful for islet transplantation.

  4. Stimulatory effect of apigenin-6-C-beta-L-fucopyranoside on insulin secretion and glycogen synthesis.

    PubMed

    Cazarolli, Luisa Helena; Folador, Poliane; Moresco, Henrique Hunger; Brighente, Inês Maria Costa; Pizzolatti, Moacir Geraldo; Silva, Fátima Regina M Barreto

    2009-11-01

    In vivo and in vitro treatments were carried out to investigate the effects of apigenin-6-C-beta-L-fucopyranoside (1), isolated from Averrhoa carambola L. (Oxalidaceae), on serum glucose and insulin levels in hyperglycemic rats as well as its effect on glycogen synthesis in normal rat soleus muscle. Apigenin-6-C-beta-L-fucopyranoside showed an acute effect on blood glucose lowering in hyperglycemic rats and stimulated glucose-induced insulin secretion. A stimulatory effect of 1 on glycogen synthesis was observed when muscles were incubated with this flavonoid and also its effect was completely nullified by pre-treatment with insulin signal transduction inhibitors. Taking this into account, the MAPK-PP1 and PI3K-GSK3 pathways are involved in the apigenin-6-C-beta-L-fucopyranoside-induced increase in glycogen synthesis in muscle. This study provides evidence for dual effects of apigenin-6-C-beta-L-fucopyranoside as an antihyperglycemic (insulin secretion) as well as an insulinomimetic (glycogen synthesis) agent.

  5. TCF7L2 Regulates Late Events in Insulin Secretion From Pancreatic Islet β-Cells

    PubMed Central

    da Silva Xavier, Gabriela; Loder, Merewyn K.; McDonald, Angela; Tarasov, Andrei I.; Carzaniga, Raffaella; Kronenberger, Katrin; Barg, Sebastian; Rutter, Guy A.

    2009-01-01

    OBJECTIVE Polymorphisms in the human TCF7L2 gene are associated with reduced insulin secretion and an increased risk of type 2 diabetes. However, the mechanisms by which TCF7L2 affect insulin secretion are still unclear. We define the effects of TCF7L2 expression level on mature β-cell function and suggest a potential mechanism for its actions. RESEARCH DESIGN AND METHODS TCF7L2 expression in rodent islets and β-cell lines was altered using RNAi or adenoviral transduction. β-Cell gene profiles were measured by quantitative real-time PCR and the effects on intracellular signaling and exocytosis by live cell imaging, electron microscopy, and patch clamp electrophysiology. RESULTS Reducing TCF7L2 expression levels by RNAi decreased glucose- but not KCl-induced insulin secretion. The glucose-induced increments in both ATP/ADP ratio and cytosolic free Ca2+ concentration ([Ca2+]i) were increased compared with controls. Overexpression of TCF7L2 exerted minor inhibitory effects on glucose-regulated changes in [Ca2+]i and insulin release. Gene expression profiling in TCF7L2-silenced cells revealed increased levels of mRNA encoding syntaxin 1A but decreased Munc18–1 and ZnT8 mRNA. Whereas the number of morphologically docked vesicles was unchanged by TCF7L2 suppression, secretory granule movement increased and capacitance changes decreased, indicative of defective vesicle fusion. CONCLUSION—TCF7L2 is involved in maintaining expression of β-cell genes regulating secretory granule fusion. Defective insulin exocytosis may thus underlie increased diabetes incidence in carriers of the at-risk TCF7L2 alleles. PMID:19168596

  6. TCF7L2 regulates late events in insulin secretion from pancreatic islet beta-cells.

    PubMed

    da Silva Xavier, Gabriela; Loder, Merewyn K; McDonald, Angela; Tarasov, Andrei I; Carzaniga, Raffaella; Kronenberger, Katrin; Barg, Sebastian; Rutter, Guy A

    2009-04-01

    Polymorphisms in the human TCF7L2 gene are associated with reduced insulin secretion and an increased risk of type 2 diabetes. However, the mechanisms by which TCF7L2 affect insulin secretion are still unclear. We define the effects of TCF7L2 expression level on mature beta-cell function and suggest a potential mechanism for its actions. TCF7L2 expression in rodent islets and beta-cell lines was altered using RNAi or adenoviral transduction. Beta-cell gene profiles were measured by quantitative real-time PCR and the effects on intracellular signaling and exocytosis by live cell imaging, electron microscopy, and patch clamp electrophysiology. Reducing TCF7L2 expression levels by RNAi decreased glucose- but not KCl-induced insulin secretion. The glucose-induced increments in both ATP/ADP ratio and cytosolic free Ca2+ concentration ([Ca2+]i) were increased compared with controls. Overexpression of TCF7L2 exerted minor inhibitory effects on glucose-regulated changes in [Ca2+]i and insulin release. Gene expression profiling in TCF7L2-silenced cells revealed increased levels of mRNA encoding syntaxin 1A but decreased Munc18-1 and ZnT8 mRNA. Whereas the number of morphologically docked vesicles was unchanged by TCF7L2 suppression, secretory granule movement increased and capacitance changes decreased, indicative of defective vesicle fusion. TCF7L2 is involved in maintaining expression of beta-cell genes regulating secretory granule fusion. Defective insulin exocytosis may thus underlie increased diabetes incidence in carriers of the at-risk TCF7L2 alleles.

  7. The prolyl isomerase Pin1 increases β-cell proliferation and enhances insulin secretion.

    PubMed

    Nakatsu, Yusuke; Mori, Keiichi; Matsunaga, Yasuka; Yamamotoya, Takeshi; Ueda, Koji; Inoue, Yuki; Mitsuzaki-Miyoshi, Keiko; Sakoda, Hideyuki; Fujishiro, Midori; Yamaguchi, Suguru; Kushiyama, Akifumi; Ono, Hiraku; Ishihara, Hisamitsu; Asano, Tomoichiro

    2017-07-14

    The prolyl isomerase Pin1 binds to the phosphorylated Ser/Thr-Pro motif of target proteins and enhances their cis-trans conversion. This report is the first to show that Pin1 expression in pancreatic β cells is markedly elevated by high-fat diet feeding and in ob/ob mice. To elucidate the role of Pin1 in pancreatic β cells, we generated β-cell-specific Pin1 KO (βPin1 KO) mice. These mutant mice showed exacerbation of glucose intolerance but had normal insulin sensitivity. We identified two independent factors underlying impaired insulin secretion in the βPin1 KO mice. Pin1 enhanced pancreatic β-cell proliferation, as indicated by a reduced β-cell mass in βPin1 KO mice compared with control mice. Moreover, a diet high in fat and sucrose failed to increase pancreatic β-cell growth in the βPin1 KO mice, an observation to which up-regulation of the cell cycle protein cyclin D appeared to contribute. The other role of Pin1 was to activate the insulin-secretory step: Pin1 KO β cells showed impairments in glucose- and KCl-induced elevation of the intracellular Ca(2+) concentration and insulin secretion. We also identified salt-inducible kinase 2 (SIK2) as a Pin1-binding protein that affected the regulation of Ca(2+) influx and found Pin1 to enhance SIK2 kinase activity, resulting in a decrease in p35 protein, a negative regulator of Ca(2+) influx. Taken together, our observations demonstrate critical roles of Pin1 in pancreatic β cells and that Pin1 both promotes β-cell proliferation and activates insulin secretion. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

  8. A beta cell ATGL-lipolysis/adipose tissue axis controls energy homeostasis and body weight via insulin secretion in mice.

    PubMed

    Attané, Camille; Peyot, Marie-Line; Lussier, Roxane; Poursharifi, Pegah; Zhao, Shangang; Zhang, Dongwei; Morin, Johane; Pineda, Marco; Wang, Shupei; Dumortier, Olivier; Ruderman, Neil B; Mitchell, Grant A; Simons, Brigitte; Madiraju, S R Murthy; Joly, Erik; Prentki, Marc

    2016-12-01

    To directly assess the role of beta cell lipolysis in insulin secretion and whole-body energy homeostasis, inducible beta cell-specific adipose triglyceride lipase (ATGL)-deficient (B-Atgl-KO) mice were studied under normal diet (ND) and high-fat diet (HFD) conditions. Atgl (flox/flox) mice were cross-bred with Mip-Cre-ERT mice to generate Mip-Cre-ERT(/+);Atgl (flox/flox) mice. At 8 weeks of age, these mice were injected with tamoxifen to induce deletion of beta cell-specific Atgl (also known as Pnpla2), and the mice were fed an ND or HFD. ND-fed male B-Atgl-KO mice showed decreased insulinaemia and glucose-induced insulin secretion (GSIS) in vivo. Changes in GSIS correlated with the islet content of long-chain saturated monoacylglycerol (MAG) species that have been proposed to be metabolic coupling factors for insulin secretion. Exogenous MAGs restored GSIS in B-Atgl-KO islets. B-Atgl-KO male mice fed an HFD showed reduced insulinaemia, glycaemia in the fasted and fed states and after glucose challenge, as well as enhanced insulin sensitivity. Moreover, decreased insulinaemia in B-Atgl-KO mice was associated with increased energy expenditure, and lipid metabolism in brown (BAT) and white (WAT) adipose tissues, leading to reduced fat mass and body weight. ATGL in beta cells regulates insulin secretion via the production of signalling MAGs. Decreased insulinaemia due to lowered GSIS protects B-Atgl-KO mice from diet-induced obesity, improves insulin sensitivity, increases lipid mobilisation from WAT and causes BAT activation. The results support the concept that fuel excess can drive obesity and diabetes via hyperinsulinaemia, and that an islet beta cell ATGL-lipolysis/adipose tissue axis controls energy homeostasis and body weight via insulin secretion.

  9. Linoleic acid decreases leptin and adiponectin secretion from primary rat adipocytes in the presence of insulin.

    PubMed

    Pérez-Matute, P; Martínez, J A; Marti, A; Moreno-Aliaga, M J

    2007-10-01

    Obesity rates have dramatically increased over the last few decades and, at the same time, major changes in the type of fatty acid intake have occurred. Linoleic acid, an n-6 polyunsaturated fatty acid, is an essential fatty acid occurring in high amounts in several western diets. A potential role of this fatty acid on obesity has been suggested. Controversial effects of linoleic acid on insulin sensitivity have also been reported. Thus, the aim of this study was to examine the direct effects of linoleic acid on leptin and adiponectin production, two adipokines known to influence weight gain and insulin sensitivity. Because insulin-stimulated glucose metabolism is an important regulator of leptin production, the effects of linoleic acid on adipocyte metabolism were also examined. For this purpose, isolated rat adipocytes were incubated with linoleic acid (1-200 microM) in the absence or presence of insulin. Linoleic acid (1-200 microM) significantly decreased insulin-stimulated leptin secretion and expression (P < 0.05), however, no changes in basal leptin production were observed. Linoleic acid also induced a significant decrease (approximately 20%) in adiponectin secretion (P < 0.05), but only in the presence of insulin and at the highest concentration tested (200 microM). This fatty acid did not modify either glucose uptake or lactate production and the percentage of glucose metabolized to lactate was not changed either. Together, these results suggest that linoleic acid seems to interfere with other insulin signalling pathway different from those controlling glucose uptake and metabolism, but involved in the regulation of leptin and adiponectin production.

  10. Recent Advances in Obesity-Induced Inflammation and Insulin Resistance

    PubMed Central

    Tateya, Sanshiro; Kim, Francis; Tamori, Yoshikazu

    2013-01-01

    It has been demonstrated in rodents and humans that chronic inflammation characterized by macrophage infiltration occurs mainly in adipose tissue or liver during obesity, in which activation of immune cells is closely associated with insulin sensitivity. Macrophages can be classified as classically activated (M1) macrophages that support microbicidal activity or alternatively activated (M2) macrophages that support allergic and antiparasitic responses. In the context of insulin action, M2 macrophages sustain insulin sensitivity by secreting IL-4 and IL-10, while M1 macrophages induce insulin resistance through the secretion of proinflammatory cytokines, such as TNFα. Polarization of M1/M2 is controlled by various dynamic functions of other immune cells. It has been demonstrated that, in a lean state, TH2 cells, Treg cells, natural killer T cells, or eosinophils contribute to the M2 activation of macrophages by secreting IL-4 or IL-10. In contrast, obesity causes alteration of the constituent immune cells, in which TH1 cells, B cells, neutrophils, or mast cells induce M1 activation of macrophages by the elevated secretion of TNFα and IFNγ. Increased secretion of TNFα and free fatty acids from hypertrophied adipocytes also contributes to the M1 activation of macrophages. Since obesity-induced insulin resistance is established by macrophage infiltration and the activation of immune cells inside tissues, identification of the factors that regulate accumulation and the intracellular signaling cascades that define polarization of M1/M2 would be indispensable. Regulation of these factors would lead to the pharmacological inhibition of obesity-induced insulin resistance. In this review, we introduce molecular mechanisms relevant to the pathophysiology and review the most recent studies of clinical applications targeting chronic inflammation. PMID:23964268

  11. Tear secretion and tear film function in insulin dependent diabetics

    PubMed Central

    Goebbels, M.

    2000-01-01

    BACKGROUND—Diabetic patients often complain of dry eye symptoms, such as burning and/or foreign body sensation. The aim of the present study was to investigate whether diabetes mellitus is correlated with tear film dysfunction and/or tear hyposecretion.
METHODS—In 86 consecutive insulin dependent diabetics with retinopathy and 84 non-diabetic controls (age and sex matched) we performed fluorophotometry of tear secretion, the Schirmer test, and impression cytology of the conjunctival epithelium and determined the tear film break up time.
RESULTS—When compared with the healthy control group diabetics showed decreased Schirmer test readings (−37%, p <0.001) and significantly more frequent and pronounced signs of conjunctival metaplasia. None of the other values differed between groups.
CONCLUSION—In insulin dependent diabetics, reflex tearing was demonstrated to be significantly decreased. In contrast, unstimulated basal tear flow and tear film break up time were found to be normal. However, a majority of insulin dependent diabetics shows distinct signs of conjunctival surface disease.

 PMID:10611093

  12. Development of a Streptozotocin-induced Diabetic Rat Model for Studies on the Effects of Cinnamon on Glucose Tolerance and Insulin Secretion

    USDA-ARS?s Scientific Manuscript database

    A streptozotocin (STZ) dose response protocol using graded doses of STZ was utilized to develop a diabetic rat model. In addition to the presence of severe basal hyperglycemia, insulin responses to oral glucose showed no change from basal in rats given more than 45 mg of STZ/kg body wt. Oral gluc...

  13. Liver enzymes are associated with hepatic insulin resistance, insulin secretion, and glucagon concentration in healthy men and women.

    PubMed

    Bonnet, Fabrice; Ducluzeau, Pierre-Henri; Gastaldelli, Amalia; Laville, Martine; Anderwald, Christian H; Konrad, Thomas; Mari, Andrea; Balkau, Beverley

    2011-06-01

    The pathophysiological mechanisms to explain the association between risk of type 2 diabetes and elevated concentrations of γ-glutamyltransferase (GGT) and alanineaminotransferase (ALT) remain poorly characterized. We explored the association of liver enzymes with peripheral and hepatic insulin resistance, insulin secretion, insulin clearance, and glucagon concentration. We studied 1,309 nondiabetic individuals from the Relationship between Insulin Sensitivity and Cardiovascular disease (RISC) study; all had a euglycemic-hyperinsulinemic clamp and an oral glucose tolerance test (OGTT) with assessment of insulin secretion and hepatic insulin extraction. The hepatic insulin resistance index was calculated in 393 individuals. In both men and women, plasma concentrations of GGT and ALT were inversely related with insulin sensitivity (M/I) (all P < 0.01). Likewise, the hepatic insulin resistance index was positively correlated with both GGT (r = 0.37, P < 0.0001, men; r = 0.36, P < 0.0001, women) and ALT (r = 0.25, P = 0.0005, men; r = 0.18, P = 0.01, women). These associations persisted in multivariable models. Increased GGT and ALT were significantly associated with higher insulin secretion rates and with both reduced endogenous clearance of insulin and hepatic insulin extraction during the OGTT (P = 0.0005 in men; P = 0.003 in women). Plasma fasting glucagon levels increased over ALT quartiles (men, quartile 4 vs. quartile 1 11.2 ± 5.1 vs. 9.3 ± 3.8 pmol/L, respectively, P = 0.0002; women, 9.0 ± 4.3 vs. 7.6 ± 3.1, P = 0.001). In healthy individuals, increased GGT and ALT were biomarkers of both systemic and hepatic insulin resistance with concomitant increased insulin secretion and decreased hepatic insulin clearance. The novel finding of a positive correlation between ALT and fasting glucagon level concentrations warrants confirmation in type 2 diabetes.

  14. Raldh3 expression in diabetic islets reciprocally regulates secretion of insulin and glucagon from pancreatic islets.

    PubMed

    Shimamura, Mitsuru; Karasawa, Hiroshi; Sakakibara, Sachiko; Shinagawa, Akira

    2010-10-08

    We have previously reported that obesity-induced diabetes developed in high-fat diet (HFD)-fed BDF1 mice. This is caused by insufficient insulin response to an excess glucose load. In this study, we have shown that the enhanced expression of retinaldehyde dehydrogenase 3 (Raldh3) causes functional disorders of pancreatic islets in diabetic mouse models. In the pancreatic islets of HFD-induced diabetic BDF1 mice and spontaneously diabetic C57BL/KsJ(db/db) mice, gene expression analysis with oligonucleotide microarray revealed a significant increase in Raldh3 expression. Exposure to a culture medium containing a higher glucose concentration (25 mM) significantly increased Raldh3 expression in murine MIN6 and alphaTC1 clone 9 cells, which derived from the α and β-cells of pancreatic islets, respectively. Overexpression of Raldh3 reduced the insulin secretion in MIN6 cells, and surprisingly, increased the glucagon secretion in alphaTC1 clone 9 cells. Furthermore, the knockdown of Raldh3 expression with siRNA decreased the glucagon secretion in alphaTC1 clone 9 cells. Raldh3 catalyzes the conversion of 13-cis retinal to 13-cis retinoic acid and we revealed that 13-cis retinoic acid significantly reduces cell viability in MIN6 and alphaTC1 clone 9 cells, but not in cells of H4IIEC3, 3T3-L1, and COS-1 cell lines. These findings suggest that an increasing expression of Raldh3 deregulates the balanced mechanisms of insulin and glucagon secretion in the pancreatic islets and may induce β-cell dysfunction leading to the development of type 2 diabetes. Copyright © 2010 Elsevier Inc. All rights reserved.

  15. The effects of sevoflurane anesthesia on insulin secretion and glucose metabolism in pigs.

    PubMed

    Saho, S; Kadota, Y; Sameshima, T; Miyao, J; Tsurumaru, T; Yoshimura, N

    1997-06-01

    We investigated the effects of two different concentrations of sevoflurane, 0.4 minimum alveolar anesthetic concentration (MAC) and 1.0 MAC, on insulin secretion before, during, and after sevoflurane anesthesia using three successive intravenous glucose tolerance tests (IVGTT) in pigs with indwelling catheters. We also investigated changes in the levels of plasma glucose, catecholamines (epinephrine [E], norepinephrine [NE]), and cortisol (Cor). The pigs were grouped as awake, 0.4 MAC, or 1.0 MAC. Sevoflurane decreased the ratio of insulin/glucose (INS/GLU) in the basal condition (P < 0.05 awake versus 1.0 MAC) and during IVGTT (P < 0.01 awake versus 1.0 MAC and 0.4 MAC). These decreases were quickly reversible (control levels were regained within 2 h of the end of anesthesia), were probably dose-related, appeared not to be mediated by E, NE, or Cor. In addition, the INS/GLU ratio 2.5-4 h after the end of anesthesia was significantly higher in the anesthetized groups than in the awake group. We conclude that sevoflurane anesthesia has a rapidly reversible inhibitory effect on basal and glucose-stimulated insulin secretion, as do other inhaled anesthetics, and might induce insulin resistance.

  16. A novel Gymnema sylvestre extract stimulates insulin secretion from human islets in vivo and in vitro.

    PubMed

    Al-Romaiyan, A; Liu, B; Asare-Anane, H; Maity, C R; Chatterjee, S K; Koley, N; Biswas, T; Chatterji, A K; Huang, G-C; Amiel, S A; Persaud, S J; Jones, P M

    2010-09-01

    Many plant-based products have been suggested as potential antidiabetic agents, but few have been shown to be effective in treating the symptoms of Type 2 diabetes mellitus (T2DM) in human studies, and little is known of their mechanisms of action. Extracts of Gymnema sylvestre (GS) have been used for the treatment of T2DM in India for centuries. The effects of a novel high molecular weight GS extract, Om Santal Adivasi, (OSA(R)) on plasma insulin, C-peptide and glucose in a small cohort of patients with T2DM are reported here. Oral administration of OSA(R) (1 g/day, 60 days) induced significant increases in circulating insulin and C-peptide, which were associated with significant reductions in fasting and post-prandial blood glucose. In vitro measurements using isolated human islets of Langerhans demonstrated direct stimulatory effects of OSA(R) on insulin secretion from human ß-cells, consistent with an in vivo mode of action through enhancing insulin secretion. These in vivo and in vitro observations suggest that OSA(R) may provide a potential alternative therapy for the hyperglycemia associated with T2DM.

  17. Inhibition of glucose-stimulated insulin secretion by KCNJ15, a newly identified susceptibility gene for type 2 diabetes.

    PubMed

    Okamoto, Koji; Iwasaki, Naoko; Doi, Kent; Noiri, Eisei; Iwamoto, Yasuhiko; Uchigata, Yasuko; Fujita, Toshiro; Tokunaga, Katsushi

    2012-07-01

    Potassium inwardly rectifying channel, subfamily J, member 15 (KCNJ15) is a type 2 diabetes-associated risk gene, and Kcnj15 overexpression suppresses insulin secretion in rat insulinoma (INS1) cells. The aim of the current study was to characterize the role of Kcnj15 by knockdown of this gene in vitro and in vivo. Human islet cells were used to determine the expression of KCNJ15. Expression of KCNJ15 mRNA in islets was higher in subjects with type 2 diabetes. In INS1 cells, Kcnj15 expression was induced by high glucose-containing medium. Regulation of Kcnj15 by glucose and its effect on insulin secretion were analyzed in INS1 cells and in normal mice and diabetic mice by the inactivation of Kcnj15 using small interfering RNA. Knockdown of Kcnj15 increased the insulin secretion in vitro and in vivo. KCNJ15 and Ca(2+)-sensing receptor (CsR) interact in the kidney. Binding of Kcnj15 with CsR was also detected in INS1 cells. In conclusion, downregulation of Kcnj15 leads to increased insulin secretion in vitro and in vivo. The mechanism to regulate insulin secretion involves KCNJ15 and CsR.

  18. Mechanisms of insulin secretion in malnutrition: modulation by amino acids in rodent models.

    PubMed

    de Oliveira, Camila Aparecida Machado; Latorraca, Márcia Queiroz; de Mello, Maria Alice Rostom; Carneiro, Everardo Magalhães

    2011-04-01

    Protein restriction at early stages of life reduces β-cell volume, number of insulin-containing granules, insulin content and release by pancreatic islets in response to glucose and other secretagogues, abnormalities similar to those seen in type 2 diabetes. Amino acids are capable to directly modulate insulin secretion and/or contribute to the maintenance of β-cell function, resulting in an improvement of insulin release. Animal models of protein malnutrition have provided important insights into the adaptive mechanisms involved in insulin secretion in malnutrition. In this review, we discuss studies focusing on the modulation of insulin secretion by amino acids, specially leucine and taurine, in rodent models of protein malnutrition. Leucine supplementation increases insulin secretion by pancreatic islets in malnourished mice. This effect is at least in part due to increase in the expression of proteins involved in the secretion process, and the activation of the PI3K/PKB/mTOR pathway seems also to contribute. Mice supplemented with taurine have increased insulin content and secretion as well as increased expression of genes essential for β-cell functionality. The knowledge of the mechanisms through which amino acids act on pancreatic β-cells to stimulate insulin secretion is of interest for clinical medicine. It can reveal new targets for the development of drugs toward the treatment of endocrine diseases, in special type 2 diabetes.

  19. A functional circadian clock is required for proper insulin secretion by human pancreatic islet cells.

    PubMed

    Saini, C; Petrenko, V; Pulimeno, P; Giovannoni, L; Berney, T; Hebrok, M; Howald, C; Dermitzakis, E T; Dibner, C

    2016-04-01

    To determine the impact of a functional human islet clock on insulin secretion and gene transcription. Efficient circadian clock disruption was achieved in human pancreatic islet cells by small interfering RNA-mediated knockdown of CLOCK. Human islet secretory function was assessed in the presence or absence of a functional circadian clock by stimulated insulin secretion assays, and by continuous around-the-clock monitoring of basal insulin secretion. Large-scale transcription analysis was accomplished by RNA sequencing, followed by quantitative RT-PCR analysis of selected targets. Circadian clock disruption resulted in a significant decrease in both acute and chronic glucose-stimulated insulin secretion. Moreover, basal insulin secretion by human islet cells synchronized in vitro exhibited a circadian pattern, which was perturbed upon clock disruption. RNA sequencing analysis suggested alterations in 352 transcript levels upon circadian clock disruption. Among them, key regulators of the insulin secretion pathway (GNAQ, ATP1A1, ATP5G2, KCNJ11) and transcripts required for granule maturation and release (VAMP3, STX6, SLC30A8) were affected. Using our newly developed experimental approach for efficient clock disruption in human pancreatic islet cells, we show for the first time that a functional β-cell clock is required for proper basal and stimulated insulin secretion. Moreover, clock disruption has a profound impact on the human islet transcriptome, in particular, on the genes involved in insulin secretion. © 2015 John Wiley & Sons Ltd.

  20. Role of cytosolic and calcium independent phospholipases A(2) in insulin secretion impairment of INS-1E cells infected by S. aureus.

    PubMed

    Caporarello, N; Salmeri, M; Scalia, M; Motta, C; Parrino, C; Frittitta, L; Olivieri, M; Toscano, M A; Anfuso, C D; Lupo, G

    2015-12-21

    Cytosolic PLA2 (cPLA2) and Ca(2+)-independent PLA2 (iPLA2) play a significant role in insulin β-cells secretion. Bacterial infections may be responsible of the onset of diabetes. The mechanism by which Staphylococcus aureus infection of INS-1 cells alters glucose-induced insulin secretion has been examined. After acute infection, insulin secretion and PLA2 activities significantly increased. Moreover, increased expressions of phospho-cPLA2, phospho-PKCα and phospho-ERK 1/2 were observed. Chronic infection causes a decrease in insulin release and a significant increase of iPLA2 and COX-2 protein expression. Moreover, insulin secretion in infected cells could be restored using specific siRNAs against iPLA2 isoform and specific COX-2 inhibitor.

  1. Pigment epithelium-derived factor (PEDF) regulates metabolism and insulin secretion from a clonal rat pancreatic beta cell line BRIN-BD11 and mouse islets.

    PubMed

    Chen, Younan; Carlessi, Rodrigo; Walz, Nikita; Cruzat, Vinicius Fernandes; Keane, Kevin; John, Abraham N; Jiang, Fang-Xu; Carnagarin, Revathy; Dass, Crispin R; Newsholme, Philip

    2016-05-05

    Pigment epithelium-derived factor (PEDF) is a multifunctional glycoprotein, associated with lipid catabolism and insulin resistance. In the present study, PEDF increased chronic and acute insulin secretion in a clonal rat β-cell line BRIN-BD11, without alteration of glucose consumption. PEDF also stimulated insulin secretion from primary mouse islets. Seahorse flux analysis demonstrated that PEDF did not change mitochondrial respiration and glycolytic function. The cytosolic presence of the putative PEDF receptor - adipose triglyceride lipase (ATGL) - was identified, and ATGL associated stimulation of glycerol release was robustly enhanced by PEDF, while intracellular ATP levels increased. Addition of palmitate or ex vivo stimulation with inflammatory mediators induced β-cell dysfunction, effects not altered by the addition of PEDF. In conclusion, PEDF increased insulin secretion in BRIN-BD11 and islet cells, but had no impact on glucose metabolism. Thus elevated lipolysis and enhanced fatty acid availability may impact insulin secretion following PEDF receptor (ATGL) stimulation.

  2. A volume-activated anion conductance in insulin-secreting cells.

    PubMed

    Best, L; Sheader, E A; Brown, P D

    1996-01-01

    The whole-cell patch-clamp recording technique was used to measure volume-activated currents in K+-free solutions in RINm5F and HIT-T15 insulinoma cells and in dispersed rat islet cells. Cell swelling, induced by intracellular hypertonicity or extracellular hypotonicity, caused activation of an outwardly rectifying conductance which could be subsequently inactivated by hypertonic extracellular solutions. The conductance required adenosine 5'-triphosphate (ATP) in the pipette solution but was Ca2+ independent. Na+ and Cl- substitution studies suggested that the swelling-activated current is Cl- selective with a halide permeability sequence of Br > Cl > I. The conductance was reversibly inhibited by the anion channel inhibitors 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and by 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB). Further evidence for a volume-activated anion conductance was provided by studies of volume regulation in insulin-secreting cells. When RINm5F cells were exposed to a hypotonic medium, the initial cell swelling was followed by a regulatory volume decrease (RVD). This RVD response was also inhibited by DIDS and by NPPB. These data therefore provide evidence for a volume-activated anion conductance in insulin-secreting cells which could be involved in the RVD following osmotic stress. A possible role for the conductance in hypotonically induced insulin release is also discussed.

  3. Regulation of insulin secretion and reactive oxygen species production by free fatty acids in pancreatic islets.

    PubMed

    Graciano, Maria Fernanda Rodrigues; Valle, Maíra M R; Kowluru, Anjan; Curi, Rui; Carpinelli, Angelo R

    2011-01-01

    Free fatty acids regulate insulin secretion through metabolic and intracellular signaling mechanisms such as induction of malonyl-CoA/long-chain CoA pathway, production of lipids, GPRs (G protein-coupled receptors) activation and the modulation of calcium currents. Fatty acids (FA) are also important inducers of ROS (reactive oxygen species) production in β-cells. Production of ROS for short periods is associated with an increase in GSIS (glucose-stimulated insulin secretion), but excessive or sustained production of ROS is negatively correlated with the insulin secretory process. Several mechanisms for FA modulation of ROS production by pancreatic β-cells have been proposed, such as the control of mitochondrial complexes and electron transport, induction of uncoupling proteins, NADPH oxidase activation, interaction with the renin-angiotensin system, and modulation of the antioxidant defense system. The major sites of superoxide production within mitochondria derive from complexes I and III. The amphiphilic nature of FA favors their incorporation into mitochondrial membranes, altering the membrane fluidity and facilitating the electron leak. The extra-mitochondrial ROS production induced by FA through the NADPH oxidase complex is also an important source of these species in β-cells.

  4. Insulin sensitivity and secretion in Arab Americans with glucose intolerance.

    PubMed

    Salinitri, Francine D; Pinelli, Nicole R; Martin, Emily T; Jaber, Linda A

    2013-12-01

    This study examined the pathophysiological abnormalities in Arab Americans with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT). Homeostasis model assessment of insulin resistance (HOMA-IR), homeostasis model assessment of insulin secretion (HOMA-%β), and the Matsuda Insulin Sensitivity Index composite (ISIcomposite) were calculated from the fasting and stimulated glucose and insulin concentrations measured during the oral glucose tolerance test in a population-based, representative, cross-sectional sample of randomly selected Arab Americans. In total, 497 individuals (42±14 years old; 40% males; body mass index [BMI], 29±6 kg/m(2)) were studied. Multivariate linear regression models were performed to compare HOMA-IR, HOMA-%β, and ISIcomposite among individuals with normal glucose tolerance (NGT) (n=191) versus isolated IFG (n=136), isolated IGT (n=22), combined IFG/IGT (n=43), and diabetes (n=105). Compared with individuals with NGT (2.9±1.6), HOMA-IR progressively increased in individuals with isolated IFG (4.8±2.7, P<0.001), combined IFG/IGT (6.0±4.3, P<0.001), and diabetes (9.7±8.3, P<0.001) but not in those with isolated IGT (3.0±1.7, P=0.87). After adjustment for sex and BMI, these associations remained unchanged. Whole-body insulin sensitivity as measured by ISIcomposite was significantly lower in individuals with isolated IFG (3.9±2.3, P<0.001), isolated IGT (2.8±1.5, P<0.001), combined IFG/IGT (1.9±1.1, P<0.001), and diabetes (1.6±1.1, P<0.001) compared with those with NGT (6.1±3.5). HOMA-%β was significantly lower in diabetes (113.7±124.9, P<0.001) compared with NGT (161.3±92.0). After adjustment for age, sex, and BMI, isolated IFG (146.6±80.2) was also significantly associated with a decline in HOMA-%β relative to NGT (P=0.005). This study suggests that differences in the underlying metabolic defects leading to diabetes in Arab Americans with IFG and/or IGT exist and may require different strategies for the

  5. Novel Zn2+ Modulated GPR39 Receptor Agonists Do Not Drive Acute Insulin Secretion in Rodents

    PubMed Central

    Yasuda, Shin-ichiro; Tsuchida, Takuma; Oguma, Takahiro; Marley, Anna; Wennberg-Huldt, Charlotte; Hovdal, Daniel; Fukuda, Hajime; Yoneyama, Yukimi; Sasaki, Kazuyo; Johansson, Anders; Lundqvist, Sara; Brengdahl, Johan; Isaacs, Richard J.; Brown, Daniel; Geschwindner, Stefan; Benthem, Lambertus; Priest, Claire; Turnbull, Andrew

    2015-01-01

    Type 2 diabetes (T2D) occurs when there is insufficient insulin release to control blood glucose, due to insulin resistance and impaired β-cell function. The GPR39 receptor is expressed in metabolic tissues including pancreatic β-cells and has been proposed as a T2D target. Specifically, GPR39 agonists might improve β-cell function leading to more adequate and sustained insulin release and glucose control. The present study aimed to test the hypothesis that GPR39 agonism would improve glucose stimulated insulin secretion in vivo. A high throughput screen, followed by a medicinal chemistry program, identified three novel potent Zn2+ modulated GPR39 agonists. These agonists were evaluated in acute rodent glucose tolerance tests. The results showed a lack of glucose lowering and insulinotropic effects not only in lean mice, but also in diet-induced obese (DIO) mice and Zucker fatty rats. It is concluded that Zn2+ modulated GPR39 agonists do not acutely stimulate insulin release in rodents. PMID:26720709

  6. Opiate-prostaglandin interactions in the regulation of insulin secretion from rat islets of Langerhans in vitro

    SciTech Connect

    Green, I.C.; Tadayyon, M.

    1988-01-01

    The inadequate insulin secretory response to glucose stimulation in non-insulin dependent diabetes has been attributed to many factors including high PGE/sub 2/ levels blunting the secretory response, and to the existence of inhibitory opiate activity in vivo. The purpose of the present work was to see if there was a connection between these two independent theories. Radioimmunoassayable PGE/sub 2/ in islets of Langerhans was found to be proportional to islet number and protein content and was typically 4 to 5pg/..mu..g islet protein. Indomethacin sodium salicylate and chlorpropamide all lowered islet PGE/sub 2/ levels and stimulated insulin release in vitro. Dynorphin stimulated insulin release at a concentration of 6 x 10/sup -9/M, while lowering islet PGE/sub 2/. Conversely, at a higher concentration, dynorphin had no stimulatory effect on insulin secretion and did not lower PGE/sub 2/ levels in islets or in the incubation media. The stimulatory effects of dynorphin and sodium salicylate on insulin secretion were blocked by exogenous PGE/sub 2/. PGE/sub 2/ at a lower concentration did not exert any inhibitory effect on dynorphin- or sodium salicylate-induced insulin release. This concentration of exogenous PGE/sub 2/ stimulated insulin release in the presence of 6mM glucose.

  7. Nitric oxide (NO)--production and regulation of insulin secretion in islets of freely fed and fasted mice.

    PubMed

    Eckersten, Dag; Henningsson, Ragnar

    2012-02-10

    Production of nitric oxide through the action of nitric oxide synthase (NOS) has been detected in the islets of Langerhans. The inducible isoform of NOS (iNOS) is induced by cytokines and might contribute to the development of type-1 diabetes, while the constitutive isoform (cNOS) is thought to be implicated in the physiological regulation of insulin secretion. In the present study we have detected and quantified islet cNOS- and iNOS-derived NO production concomitant with measuring its influence on insulin secretion in the presence of different secretagogues: glucose, L-arginine, L-leucine and α-ketoisocaproic acid (KIC) both during fasting and freely fed conditions. In intact islets from freely fed mice both cNOS- and iNOS-activity was greatly increased by glucose (20 mmol/l). Fasting induced islet iNOS activity at both physiological (7 mmol/l) and high (20 mmol/l) glucose concentrations. NOS blockade increased insulin secretion both during freely fed conditions and after fasting. L-arginine stimulated islet cNOS activity and did not affect islet iNOS activity. l-leucine or KIC, known to enter the TCA cycle without affecting glycolysis, did not affect either islet cNOS- or iNOS activity. Accordingly, insulin secretion stimulated by L-leucine or KIC was unaffected by addition of L-NAME both during feeding and fasting. We conclude that both high glucose concentrations and fasting increase islet total NO production (mostly iNOS derived) which inhibit insulin secretion. The insulin secretagogues L-leucine and KIC, which do not affect glycolysis, do not interfere with the islet NO-NOS system.

  8. Weight-dependent differential contribution of insulin secretion and clearance to hyperinsulinemia of obesity.

    PubMed

    Erdmann, Johannes; Mayr, Martina; Oppel, Ulrich; Sypchenko, Oleg; Wagenpfeil, Stefan; Schusdziarra, Volker

    2009-01-08

    Obesity is associated with insulin resistance and the resulting hyperinsulinemia has been attributed to an increase of insulin secretion and a reduction of insulin clearance. The present study was intended to further characterize the relative contribution of secretion and clearance especially in the postprandial state. In relation to WHO body weight classes 291 subjects were divided in 5 subgroups Basal insulin concentrations rose stepwise and significantly with increasing BMI. This was paralleled by C-peptide concentrations and insulin secretion, while the reduction of insulin clearance was less stringent in relation to BMI. Basal glucose was unchanged in the BMI25 group and 8% higher in the obese groups (BMI 30, 35, 40) compared to normal weight (NW). Although postprandial insulin concentrations were significantly higher in the overweight and obese groups compared to NW the correlation was not as tight as in the basal state. Furthermore, the present data demonstrate for the first time that insulin secretion only increased in the overweight group without further augmentation in the obese groups. Further hyperinsulinemia of the latter was due to weight-dependent reduction of insulin clearance. The postprandial glucose response was 38-82% higher with increasing weight compared to NW. In summary basal hyperinsulinemia is mainly due to weight related increase of insulin secretion with moderate contribution of reduced insulin clearance. Postprandially, hyperinsulinemia of overweight is predominantly due to secretion while further postprandial hyperinsulinemia of obese subjects is mainly due to reduced clearance. Thus, postprandial insulin secretion cannot respond adequately to the challenge of weight-dependent insulin resistance already in non-diabetic obese subjects.

  9. Insulin signal transduction pathways and insulin-induced gene expression.

    PubMed

    Keeton, Adam B; Amsler, Maggie O; Venable, Derwei Y; Messina, Joseph L

    2002-12-13

    Insulin regulates metabolic activity, gene transcription, and cell growth by modulating the activity of several intracellular signaling pathways. Insulin activation of one mitogen-activated protein kinase cascade, the MEK/ERK kinase cascade, is well described. However, the effect of insulin on the parallel p38 pathway is less well understood. The present work examines the effect of inhibiting the p38 signaling pathway by use of specific inhibitors, either alone or in combination with insulin, on the activation of ERK1/2 and on the regulation of gene transcription in rat hepatoma cells. Activation of ERK1/2 was induced by insulin and was dependent on the activation of MEK1, the kinase upstream of ERK in this pathway. Treatment of cells with p38 inhibitors also induced ERK1/2 activation/phosphorylation. The addition of p38 inhibitors followed by insulin addition resulted in a greater than additive activation of ERK1/2. The two genes studied, c-Fos and Pip92, are immediate-early genes that are dependent on the ERK1/2 pathway for insulin-regulated induction because the insulin effect was inhibited by pretreatment with a MEK1 inhibitor. The addition of p38 inhibitors induced transcription of both genes in a dose-dependent manner, and insulin stimulation of both genes was enhanced by prior treatment with p38 inhibitors. The ability of the p38 inhibitors to induce ERK1/2 and gene transcription, both alone and in combination with insulin, was abolished by prior inhibition of MEK1. These data suggest possible cross-talk between the p38 and ERK1/2 signaling pathways and a potential role of p38 in insulin signaling.

  10. The voltage-gated proton channel Hv1 is expressed in pancreatic islet β-cells and regulates insulin secretion.

    PubMed

    Zhao, Qing; Che, Yongzhe; Li, Qiang; Zhang, Shangrong; Gao, Ying-Tang; Wang, Yifan; Wang, Xudong; Xi, Wang; Zuo, Weiyan; Li, Shu Jie

    2015-12-25

    The voltage-gated proton channel Hv1 is a potent acid extruder that participates in the extrusion of the intracellular acid. Here, we showed for the first time, Hv1 is highly expressed in mouse and human pancreatic islet β-cells, as well as β-cell lines. Imaging studies demonstrated that Hv1 resides in insulin-containing granules in β-cells. Knockdown of Hv1 with RNA interference significantly reduces glucose- and K(+)-induced insulin secretion in isolated islets and INS-1 (832/13) β-cells and has an impairment on glucose- and K(+)-induced intracellular Ca(2+) homeostasis. Our data demonstrated that the expression of Hv1 in pancreatic islet β-cells regulates insulin secretion through regulating Ca(2+) homeostasis.

  11. The voltage-gated proton channel Hv1 is expressed in pancreatic islet β-cells and regulates insulin secretion

    SciTech Connect

    Zhao, Qing; Che, Yongzhe; Li, Qiang; Zhang, Shangrong; Gao, Ying-Tang; Wang, Yifan; Wang, Xudong; Xi, Wang; Zuo, Weiyan; Li, Shu Jie

    2015-12-25

    The voltage-gated proton channel Hv1 is a potent acid extruder that participates in the extrusion of the intracellular acid. Here, we showed for the first time, Hv1 is highly expressed in mouse and human pancreatic islet β-cells, as well as β-cell lines. Imaging studies demonstrated that Hv1 resides in insulin-containing granules in β-cells. Knockdown of Hv1 with RNA interference significantly reduces glucose- and K{sup +}-induced insulin secretion in isolated islets and INS-1 (832/13) β-cells and has an impairment on glucose- and K{sup +}-induced intracellular Ca{sup 2+} homeostasis. Our data demonstrated that the expression of Hv1 in pancreatic islet β-cells regulates insulin secretion through regulating Ca{sup 2+} homeostasis.

  12. Senescence marker protein-30/gluconolactonase deletion worsens glucose tolerance through impairment of acute insulin secretion.

    PubMed

    Hasegawa, Goji; Yamasaki, Masahiro; Kadono, Mayuko; Tanaka, Muhei; Asano, Mai; Senmaru, Takafumi; Kondo, Yoshitaka; Fukui, Michiaki; Obayashi, Hiroshi; Maruyama, Naoki; Nakamura, Naoto; Ishigami, Akihito

    2010-02-01

    Senescence marker protein-30 (SMP30) is an androgen-independent factor that decreases with age. We recently identified SMP30 as the lactone-hydrolyzing enzyme gluconolactonase (GNL), which is involved in vitamin C biosynthesis in animal species. To examine whether the age-related decrease in SMP30/GNL has effects on glucose homeostasis, we used SMP30/GNL knockout (KO) mice treated with L-ascorbic acid. In an ip glucose tolerance test at 15 wk of age, blood glucose levels in SMP30/GNL KO mice were significantly increased by 25% at 30 min after glucose administration compared with wild-type (WT) mice. Insulin levels in SMP30/GNL KO mice were significantly decreased by 37% at 30 min after glucose compared with WT mice. Interestingly, an insulin tolerance test showed a greater glucose-lowering effect in SMP30/GNL KO mice. High-fat diet feeding severely worsened glucose tolerance in both WT and SMP30/GNL KO mice. Morphometric analysis revealed no differences in the degree of high-fat diet-induced compensatory increase in beta-cell mass and proliferation. In the static incubation study of islets, insulin secretion in response to 20 mm glucose or KCl was significantly decreased in SMP30/GNL KO mice. On the other hand, islet ATP content at 20 mm in SMP30/GNL KO mice was similar to that in WT mice. Collectively, these data indicate that impairment of the early phase of insulin secretion due to dysfunction of the distal portion of the secretion pathway underlies glucose intolerance in SMP30/GNL KO mice. Decreased SMP30/GNL may contribute to the worsening of glucose tolerance that occurs in normal aging.

  13. Decreased STARD10 Expression Is Associated with Defective Insulin Secretion in Humans and Mice.

    PubMed

    Carrat, Gaelle R; Hu, Ming; Nguyen-Tu, Marie-Sophie; Chabosseau, Pauline; Gaulton, Kyle J; van de Bunt, Martijn; Siddiq, Afshan; Falchi, Mario; Thurner, Matthias; Canouil, Mickaël; Pattou, Francois; Leclerc, Isabelle; Pullen, Timothy J; Cane, Matthew C; Prabhala, Priyanka; Greenwald, William; Schulte, Anke; Marchetti, Piero; Ibberson, Mark; MacDonald, Patrick E; Manning Fox, Jocelyn E; Gloyn, Anna L; Froguel, Philippe; Solimena, Michele; McCarthy, Mark I; Rutter, Guy A

    2017-02-02

    Genetic variants near ARAP1 (CENTD2) and STARD10 influence type 2 diabetes (T2D) risk. The risk alleles impair glucose-induced insulin secretion and, paradoxically but characteristically, are associated with decreased proinsulin:insulin ratios, indicating improved proinsulin conversion. Neither the identity of the causal variants nor the gene(s) through which risk is conferred have been firmly established. Whereas ARAP1 encodes a GTPase activating protein, STARD10 is a member of the steroidogenic acute regulatory protein (StAR)-related lipid transfer protein family. By integrating genetic fine-mapping and epigenomic annotation data and performing promoter-reporter and chromatin conformational capture (3C) studies in β cell lines, we localize the causal variant(s) at this locus to a 5 kb region that overlaps a stretch-enhancer active in islets. This region contains several highly correlated T2D-risk variants, including the rs140130268 indel. Expression QTL analysis of islet transcriptomes from three independent subject groups demonstrated that T2D-risk allele carriers displayed reduced levels of STARD10 mRNA, with no concomitant change in ARAP1 mRNA levels. Correspondingly, β-cell-selective deletion of StarD10 in mice led to impaired glucose-stimulated Ca(2+) dynamics and insulin secretion and recapitulated the pattern of improved proinsulin processing observed at the human GWAS signal. Conversely, overexpression of StarD10 in the adult β cell improved glucose tolerance in high fat-fed animals. In contrast, manipulation of Arap1 in β cells had no impact on insulin secretion or proinsulin conversion in mice. This convergence of human and murine data provides compelling evidence that the T2D risk associated with variation at this locus is mediated through reduction in STARD10 expression in the β cell. Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.

  14. The good and bad effects of statins on insulin sensitivity and secretion.

    PubMed

    Muscogiuri, Giovanna; Sarno, Gerardo; Gastaldelli, Amalia; Savastano, Silvia; Ascione, Antonio; Colao, Annamaria; Orio, Francesco

    2014-01-01

    Statins are the main lipid-lowering treatment in both primary and secondary prevention populations. Whether statins deteriorates glycemic control, predisposing to the onset of diabetes mellitus has been a matter of recent concern. Statins may accelerate progression to diabetes via molecular mechanisms that impact insulin sensitivity and secretion. In this review, we debate the relative effect of statins in driving insulin resistance and the impairment of insulin secretion. Narrative overview of the literature synthesizing the findings of literature was retrieved from searches of computerized databases, hand searches, and authoritative texts employing the key words "Statins", "Randomized Clinical Trial", "Insulin sensitivity", "Insulin resistance", "Insulin Secretion", "Diabetes Mellitus" alone and/or in combination. The weight of clinical evidence suggests a worsening effect of statins on insulin resistance and secretion, anyway basic science studies did not find a clear molecular explanation, providing conflicting evidence regarding both the beneficial and the adverse effects of statin therapy on insulin sensitivity. Although most of the clinical studies suggest a worsening of insulin resistance and secretion, the cardiovascular benefits of statin therapy outweigh the risk of developing insulin resistance, thus the data suggest the need to treat dyslipidemia and to make patients aware of the possible risk of developing type 2 diabetes or, if they already are diabetic, of worsening their metabolic control.

  15. Insulin’s direct hepatic effect explains the inhibition of glucose production caused by insulin secretion

    PubMed Central

    Edgerton, Dale S.; Kraft, Guillaume; Smith, Marta; Farmer, Ben; Williams, Phillip E.; Coate, Katie C.; Printz, Richard L.; O’Brien, Richard M.; Cherrington, Alan D.

    2017-01-01

    Insulin can inhibit hepatic glucose production (HGP) by acting directly on the liver as well as indirectly through effects on adipose tissue, pancreas, and brain. While insulin’s indirect effects are indisputable, their physiologic role in the suppression of HGP seen in response to increased insulin secretion is not clear. Likewise, the mechanisms by which insulin suppresses lipolysis and pancreatic α cell secretion under physiologic circumstances are also debated. In this study, insulin was infused into the hepatic portal vein to mimic increased insulin secretion, and insulin’s indirect liver effects were blocked either individually or collectively. During physiologic hyperinsulinemia, plasma free fatty acid (FFA) and glucagon levels were clamped at basal values and brain insulin action was blocked, but insulin’s direct effects on the liver were left intact. Insulin was equally effective at suppressing HGP when its indirect effects were absent as when they were present. In addition, the inhibition of lipolysis, as well as glucagon and insulin secretion, did not require CNS insulin action or decreased plasma FFA. This indicates that the rapid suppression of HGP is attributable to insulin’s direct effect on the liver and that its indirect effects are redundant in the context of a physiologic increase in insulin secretion. PMID:28352665

  16. Role of Epac2A/Rap1 signaling in interplay between incretin and sulfonylurea in insulin secretion.

    PubMed

    Takahashi, Harumi; Shibasaki, Tadao; Park, Jae-Hyung; Hidaka, Shihomi; Takahashi, Toshimasa; Ono, Aika; Song, Dae-Kyu; Seino, Susumu

    2015-04-01

    Incretin-related drugs and sulfonylureas are currently used worldwide for the treatment of type 2 diabetes. We recently found that Epac2A, a cAMP binding protein having guanine nucleotide exchange activity toward Rap, is a target of both incretin and sulfonylurea. This suggests the possibility of interplay between incretin and sulfonylurea through Epac2A/Rap1 signaling in insulin secretion. In this study, we examined the combinatorial effects of incretin and various sulfonylureas on insulin secretion and activation of Epac2A/Rap1 signaling. A strong augmentation of insulin secretion by combination of GLP-1 and glibenclamide or glimepiride, which was found in Epac2A(+/+) mice, was markedly reduced in Epac2A(-/-) mice. In contrast, the combinatorial effect of GLP-1 and gliclazide was rather mild, and the effect was not altered by Epac2A ablation. Activation of Rap1 was enhanced by the combination of an Epac-selective cAMP analog with glibenclamide or glimepiride but not gliclazide. In diet-induced obese mice, ablation of Epac2A reduced the insulin secretory response to coadministration of the GLP-1 receptor agonist liraglutide and glimepiride. These findings clarify the critical role of Epac2A/Rap1 signaling in the augmenting effect of incretin and sulfonylurea on insulin secretion and provide the basis for the effects of combination therapies of incretin-related drugs and sulfonylureas.

  17. Mitochondrial Glutamate Carrier GC1 as a Newly Identified Player in the Control of Glucose-stimulated Insulin Secretion*

    PubMed Central

    Casimir, Marina; Lasorsa, Francesco M.; Rubi, Blanca; Caille, Dorothée; Palmieri, Ferdinando; Meda, Paolo; Maechler, Pierre

    2009-01-01

    The SLC25 carrier family mediates solute transport across the inner mitochondrial membrane, a process that is still poorly characterized regarding both the mechanisms and proteins implicated. This study investigated mitochondrial glutamate carrier GC1 in insulin-secreting β-cells. GC1 was cloned from insulin-secreting cells, and sequence analysis revealed hydropathy profile of a six-transmembrane protein, characteristic of mitochondrial solute carriers. GC1 was found to be expressed at the mRNA and protein levels in INS-1E β-cells and pancreatic rat islets. Immunohistochemistry showed that GC1 was present in mitochondria, and ultrastructural analysis by electron microscopy revealed inner mitochondrial membrane localization of the transporter. Silencing of GC1 in INS-1E β-cells, mediated by adenoviral delivery of short hairpin RNA, reduced mitochondrial glutamate transport by 48% (p < 0.001). Insulin secretion at basal 2.5 mm glucose and stimulated either by intermediate 7.5 mm glucose or non-nutrient 30 mm KCl was not modified by GC1 silencing. Conversely, insulin secretion stimulated with optimal 15 mm glucose was reduced by 23% (p < 0.005) in GC1 knocked down cells compared with controls. Adjunct of cell-permeant glutamate (5 mm dimethyl glutamate) fully restored the secretory response at 15 mm glucose (p < 0.005). Kinetics of insulin secretion were investigated in perifused isolated rat islets. GC1 silencing in islets inhibited the secretory response induced by 16.7 mm glucose, both during first (−25%, p < 0.05) and second (−33%, p < 0.05) phases. This study demonstrates that insulin-secreting cells depend on GC1 for maximal glucose response, thereby assigning a physiological function to this newly identified mitochondrial glutamate carrier. PMID:19584051

  18. Effects of Tocotrienols on Insulin Secretion-Associated Genes Expression of Rat Pancreatic Islets in a Dynamic Culture

    PubMed Central

    Chia, Ling L.; Jantan, Ibrahim; Chua, Kien H.; Lam, Kok W.; Rullah, Kamal; Aluwi, Mohd F. M.

    2016-01-01

    Tocotrienols (T3) are well-known for their antioxidant properties besides showing therapeutic potential in clinical complications such as hyperlipidemia induced by diabetes. The aim of this study was to determine the effects of δ-T3, γ-T3, and α-T3 on insulin secretion-associated genes expression of rat pancreatic islets in a dynamic culture. Pancreatic islets freshly isolated from male Wistar rats were treated with T3 for 1 h at 37°C in a microfluidic system with continuous operation. The cells were collected for total RNA extraction and reverse-transcribed, followed by measurement of insulin secretion-associated genes expression using quantitative real-time polymerase chain reaction. Molecular docking experiments were performed to gain insights on how the T3 bind to the receptors. Short-term exposure of δ- and γ-T3 to pancreatic β cells in a stimulant glucose condition (16.7 mM) significantly regulated preproinsulin mRNA levels and insulin gene transcription. In contrast, α-T3 possessed less ability in the activation of insulin synthesis level. Essentially, potassium chloride (KCl), a β cell membrane depolarising agent added into the treatment further enhanced the insulin production. δ- and γ-T3 revealed significantly higher quantitative expression in most of the insulin secretion-associated genes groups containing 16.7 mM glucose alone and 16.7 mM glucose with 30 mM KCl ranging from 600 to 1200 μM (p < 0.05). The findings suggest the potential of δ-T3 in regulating insulin synthesis and glucose-stimulated insulin secretion through triggering pathway especially in the presence of KCl. PMID:27625609

  19. Chronic intermittent hypoxia disturbs insulin secretion and causes pancreatic injury via the MAPK signaling pathway.

    PubMed

    Wang, Yeying; Hai, Bing; Niu, Xiaoqun; Ai, Li; Cao, Yu; Li, Ran; Li, Yongxia

    2017-06-01

    Obstructive sleep apnea (OSA) is a breathing disorder during sleep, with a most prominent character of chronic intermittent hypoxia (CIH), which induces the generation of reactive oxygen species (ROS) that damages multiple tissues and causes metabolic disorders. In this study, we established a rat model of varying OSA with different grades of CIH (12.5% O2, 10% O2, 7.5% O2, and 5% O2) for 12 weeks, and found that CIH stimulated insulin secretion, reduced the insulin:proinsulin ratio in pancreatic tissue, and caused pancreatic tissue lesions and cell apoptosis in a dose-dependent manner. Moreover, CIH promoted the production of tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6, and activated mitogen-activated protein kinase (MAPK) family members, extracellular regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), and P38, depending on the O2 concentration. In summary, CIH disturbed insulin secretion, and caused inflammation, lesions, and cell apoptosis in pancreatic tissue via the MAPK signaling pathway, which may be of great significance for clinical treatment of OSA and type 2 diabetes mellitus (T2DM).

  20. Enhanced insulin sensitivity mediated by adipose tissue browning perturbs islet morphology and hormone secretion in response to autonomic nervous activation in female mice.

    PubMed

    Omar, Bilal A; Kvist-Reimer, Martina; Enerbäck, Sven; Ahrén, Bo

    2016-01-01

    Insulin resistance results in a compensatory increase in insulin secretion to maintain normoglycemia. Conversely, high insulin sensitivity results in reduced insulin secretion to prevent hypoglycemia. The mechanisms for this inverse adaptation are not well understood. We utilized highly insulin-sensitive mice, due to adipocyte-specific overexpression of the FOXC2 transcription factor, to study mechanisms of the reversed islet adaptation to increased insulin sensitivity. We found that Foxc2TG mice responded to mild hyperglycemia with insulin secretion significantly lower than that of wild-type mice; however, when severe hyperglycemia was induced, Foxc2TG mice demonstrated insulin secretion equal to or greater than that of wild-type mice. In response to autonomic nervous activation by 2-deoxyglucose, the acute suppression of insulin seen in wild-type mice was absent in Foxc2TG mice, suggesting impaired sympathetic signaling to the islet. Basal glucagon was increased in Foxc2TG mice, but they displayed severely impaired glucagon responses to cholinergic and autonomic nervous stimuli. These data suggest that the autonomic nerves contribute to the islet adaptation to high insulin sensitivity, which is compatible with a neuro-adipo regulation of islet function being instrumental for maintaining glucose regulation.

  1. Dopamine-Mediated Autocrine Inhibitory Circuit Regulating Human Insulin Secretion in Vitro

    PubMed Central

    Simpson, Norman; Maffei, Antonella; Freeby, Matthew; Burroughs, Steven; Freyberg, Zachary; Javitch, Jonathan; Leibel, Rudolph L.

    2012-01-01

    We describe a negative feedback autocrine regulatory circuit for glucose-stimulated insulin secretion in purified human islets in vitro. Using chronoamperometry and in vitro glucose-stimulated insulin secretion measurements, evidence is provided that dopamine (DA), which is loaded into insulin-containing secretory granules by vesicular monoamine transporter type 2 in human β-cells, is released in response to glucose stimulation. DA then acts as a negative regulator of insulin secretion via its action on D2R, which are also expressed on β-cells. We found that antagonism of receptors participating in islet DA signaling generally drive increased glucose-stimulated insulin secretion. These in vitro observations may represent correlates of the in vivo metabolic changes associated with the use of atypical antipsychotics, such as increased adiposity. PMID:22915827

  2. Effect of lipids on insulin, growth hormone and exocrine pancreatic secretion in man.

    PubMed

    Raptis, S; Dollinger, H C; von Berger, L; Kissing, J; Schröder, K E; Klör, U; Pfeiffer, E F

    1975-11-21

    Influences of fat on release of insulin, growth hormone and pancreatic enzyme secretion were studied in 35 metabolically healthy subjects. A fat solution containing 40 g of soy bean oil was administered, I.V., orally and intraduodenally. In all cases there was a similar increase of insulin but the rise in serum insulin after oral or intraduodenal fat administration was not related to the changes in plasma free fatty acids, free glycerol and triglyceride levels. Blood surgar responded according to insulin secretion. The route of fat administration may possibly influence growth hormone secretion. Following intraduodenal fat administration volume and bicarbonate contents of the duodenal juice rose slightly whereas trypsin and bilirubin content increased considerably. These results suggest that insulin secretion after oral or intraduodenal administration of fat is influenced by intestinal factors. Cholecystokinin-pancroezymin and gastric inhibitory polypeptide are qualified to serve as such factors.

  3. GPR54 peptide agonists stimulate insulin secretion from murine, porcine and human islets.

    PubMed

    Bowe, James E; Foot, Victoria L; Amiel, Stephanie A; Huang, Gao Cai; Lamb, Morgan W; Lakey, Jonathan; Jones, Peter M; Persaud, Shanta J

    2012-01-01

    This study was designed to determine the effects of 10 and 13 amino acid forms of kisspeptin on dynamic insulin secretion from mammalian islets since it is not clear from published data whether the shorter peptide is stimulatory while the longer peptide inhibits insulin release. Insulin secretion was measured by radioimmunoassay following perifusion of human, pig, rat and mouse isolated islets with kisspeptin-10 or kisspeptin-13 in the presence of 20 mM glucose. Both peptides stimulated rapid, reversible potentiation of glucose-stimulated insulin secretion from islets of all species tested. These data indicate that both kisspeptin-10 and kisspeptin-13, which is an extension of kisspeptin-10 by three amino acids, act directly at islet β-cells of various species to potentiate insulin secretion, and suggest that inhibitory effects reported in earlier studies may reflect differences in experimental protocols.

  4. Increased androgen levels in rats impair glucose-stimulated insulin secretion through disruption of pancreatic beta cell mitochondrial function.

    PubMed

    Wang, Hongdong; Wang, Xiaping; Zhu, Yunxia; Chen, Fang; Sun, Yujie; Han, Xiao

    2015-11-01

    Although insulin resistance is recognized to contribute to the reproductive and metabolic phenotypes of polycystic ovary syndrome (PCOS), pancreatic beta cell dysfunction plays an essential role in the progression from PCOS to the development of type 2 diabetes. However, the role of insulin secretory abnormalities in PCOS has received little attention. In addition, the precise changes in beta cells and the underlying mechanisms remain unclear. In this study, we therefore attempted to elucidate potential mechanisms involved in beta cell alterations in a rat model of PCOS. Glucose-induced insulin secretion was measured in islets isolated from DHT-treated and control rats. Oxygen consumption rate (OCR), ATP production, and mitochondrial copy number were assayed to evaluate mitochondrial function. Glucose-stimulated insulin secretion is significantly decreased in islets from DHT-treated rats. On the other hand, significant reductions are observed in the expression levels of several key genes involved in mitochondrial biogenesis and in mitochondrial OCR and ATP production in DHT-treated rat islets. Meanwhile, we found that androgens can directly impair beta cell function by inducing mitochondrial dysfunction in vitro in an androgen receptor dependent manner. For the first time, our study demonstrates that increased androgens in female rats can impair glucose-stimulated insulin secretion partly through disruption of pancreatic beta cell mitochondrial function. This work has significance for hyperandrogenic women with PCOS: excess activation of the androgen receptor by androgens may provoke beta cell dysfunction via mitochondrial dysfunction.

  5. Quantitative visualization of synchronized insulin secretion from 3D-cultured cells.

    PubMed

    Suzuki, Takahiro; Kanamori, Takao; Inouye, Satoshi

    2017-05-13

    Quantitative visualization of synchronized insulin secretion was performed in an isolated rat pancreatic islet and a spheroid of rat pancreatic beta cell line using a method of video-rate bioluminescence imaging. Video-rate images of insulin secretion from 3D-cultured cells were obtained by expressing the fusion protein of insulin and Gaussia luciferase (Insulin-GLase). A subclonal rat INS-1E cell line stably expressing Insulin-GLase, named iGL, was established and a cluster of iGL cells showed oscillatory insulin secretion that was completely synchronized in response to high glucose. Furthermore, we demonstrated the effect of an antidiabetic drug, glibenclamide, on synchronized insulin secretion from 2D- and 3D-cultured iGL cells. The amount of secreted Insulin-GLase from iGL cells was also determined by a luminometer. Thus, our bioluminescence imaging method could generally be used for investigating protein secretion from living 3D-cultured cells. In addition, iGL cell line would be valuable for evaluating antidiabetic drugs. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

  6. Gαo Represses Insulin Secretion by Reducing Vesicular Docking in Pancreatic β-Cells

    PubMed Central

    Zhao, Aizhen; Ohara-Imaizumi, Mica; Brissova, Marcella; Benninger, Richard K.P.; Xu, Yanwen; Hao, Yuhan; Abramowitz, Joel; Boulay, Guylain; Powers, Alvin C.; Piston, David; Jiang, Meisheng; Nagamatsu, Shinya; Birnbaumer, Lutz; Gu, Guoqiang

    2010-01-01

    OBJECTIVE Pertussis toxin uncoupling–based studies have shown that Gαi and Gαo can inhibit insulin secretion in pancreatic β-cells. Yet it is unclear whether Gαi and Gαo operate through identical mechanisms and how these G-protein–mediated signals inhibit insulin secretion in vivo. Our objective is to examine whether/how Gαo regulates islet development and insulin secretion in β-cells. RESEARCH DESIGN AND METHODS Immunoassays were used to analyze the Gαo expression in mouse pancreatic cells. Gαo was specifically inactivated in pancreatic progenitor cells by pancreatic cell–specific gene deletion. Hormone expression and insulin secretion in response to different stimuli were assayed in vivo and in vitro. Electron microscope and total internal reflection fluorescence–based assays were used to evaluate how Gαo regulates insulin vesicle docking and secretion in response to glucose stimulation. RESULTS Islet cells differentiate properly in Gαo−/− mutant mice. Gαo inactivation significantly enhances insulin secretion both in vivo and in isolation. Gαo nullizygous β-cells contain an increased number of insulin granules docked on the cell plasma membrane, although the total number of vesicles per β-cell remains unchanged. CONCLUSIONS Gαo is not required for endocrine islet cell differentiation, but it regulates the number of insulin vesicles docked on the β-cell membrane. PMID:20622165

  7. Synaptotagmin-7 phosphorylation mediates GLP-1-dependent potentiation of insulin secretion from β-cells.

    PubMed

    Wu, Bingbing; Wei, Shunhui; Petersen, Natalia; Ali, Yusuf; Wang, Xiaorui; Bacaj, Taulant; Rorsman, Patrik; Hong, Wanjin; Südhof, Thomas C; Han, Weiping

    2015-08-11

    Glucose stimulates insulin secretion from β-cells by increasing intracellular Ca(2+). Ca(2+) then binds to synaptotagmin-7 as a major Ca(2+) sensor for exocytosis, triggering secretory granule fusion and insulin secretion. In type-2 diabetes, insulin secretion is impaired; this impairment is ameliorated by glucagon-like peptide-1 (GLP-1) or by GLP-1 receptor agonists, which improve glucose homeostasis. However, the mechanism by which GLP-1 receptor agonists boost insulin secretion remains unclear. Here, we report that GLP-1 stimulates protein kinase A (PKA)-dependent phosphorylation of synaptotagmin-7 at serine-103, which enhances glucose- and Ca(2+)-stimulated insulin secretion and accounts for the improvement of glucose homeostasis by GLP-1. A phospho-mimetic synaptotagmin-7 mutant enhances Ca(2+)-triggered exocytosis, whereas a phospho-inactive synaptotagmin-7 mutant disrupts GLP-1 potentiation of insulin secretion. Our findings thus suggest that synaptotagmin-7 is directly activated by GLP-1 signaling and may serve as a drug target for boosting insulin secretion. Moreover, our data reveal, to our knowledge, the first physiological modulation of Ca(2+)-triggered exocytosis by direct phosphorylation of a synaptotagmin.

  8. Acute suppression of apo B secretion by insulin occurs independently of MTP.

    PubMed

    Sparks, Janet D; Chamberlain, Jeffrey M; O'Dell, Colleen; Khatun, Irani; Hussain, M Mahmood; Sparks, Charles E

    2011-03-11

    Secretion of apolipoprotein (apo) B-containing lipoproteins by the liver depends mainly upon apo B availability and microsomal triglyceride transfer protein (MTP) activity and is subject to insulin regulation. Hepatic MTP mRNA expression is negatively regulated by insulin which correlates with inhibition of apo B secretion suggesting that insulin might suppress apo B secretion through an MTP-dependent mechanism. To investigate this possibility, we examined the acute effect of insulin on hepatic MTP expression and activity levels in vivo utilizing apobec-1(-/-) mice. Insulin did not significantly alter hepatic MTP mRNA levels or lipid transfer activity 2h following injection, but suppressed expression of genes important in gluconeogenesis. To study the specific role of MTP, we expressed human MTP (hMTP) in primary rat hepatocytes using adenoviral gene transfer. Increased expression of hMTP resulted in a 47.6±17.9% increase in total apo B secreted. Incubation of hepatocytes with insulin suppressed apo B secretion by 50.1±10.8% in cells over-expressing hMTP and by 53.0±12.4% in control transfected hepatocytes. Results indicate that even under conditions of increased hepatic apo B secretion mediated by MTP, responsiveness of hepatocytes to insulin to suppress apo B secretion is maintained.

  9. A single-islet microplate assay to measure mouse and human islet insulin secretion.

    PubMed

    Truchan, Nathan A; Brar, Harpreet K; Gallagher, Shannon J; Neuman, Joshua C; Kimple, Michelle E

    2015-01-01

    One complication to comparing β-cell function among islet preparations, whether from genetically identical or diverse animals or human organ donors, is the number of islets required per assay. Islet numbers can be limiting, meaning that fewer conditions can be tested; other islet measurements must be excluded; or islets must be pooled from multiple animals/donors for each experiment. Furthermore, pooling islets negates the possibility of performing single-islet comparisons. Our aim was to validate a 96-well plate-based single islet insulin secretion assay that would be as robust as previously published methods to quantify glucose-stimulated insulin secretion from mouse and human islets. First, we tested our new assay using mouse islets, showing robust stimulation of insulin secretion 24 or 48 h after islet isolation. Next, we utilized the assay to quantify mouse islet function on an individual islet basis, measurements that would not be possible with the standard pooled islet assay methods. Next, we validated our new assay using human islets obtained from the Integrated Islet Distribution Program (IIDP). Human islets are known to have widely varying insulin secretion capacity, and using our new assay we reveal biologically relevant factors that are significantly correlated with human islet function, whether displayed as maximal insulin secretion response or fold-stimulation of insulin secretion. Overall, our results suggest this new microplate assay will be a useful tool for many laboratories, expert or not in islet techniques, to be able to precisely quantify islet insulin secretion from their models of interest.

  10. Brain glucagon-like peptide–1 increases insulin secretion and muscle insulin resistance to favor hepatic glycogen storage

    PubMed Central

    Knauf, Claude; Cani, Patrice D.; Perrin, Christophe; Iglesias, Miguel A.; Maury, Jean François; Bernard, Elodie; Benhamed, Fadilha; Grémeaux, Thierry; Drucker, Daniel J.; Kahn, C. Ronald; Girard, Jean; Tanti, Jean François; Delzenne, Nathalie M.; Postic, Catherine; Burcelin, Rémy

    2005-01-01

    Intestinal glucagon-like peptide–1 (GLP-1) is a hormone released into the hepatoportal circulation that stimulates pancreatic insulin secretion. GLP-1 also acts as a neuropeptide to control food intake and cardiovascular functions, but its neural role in glucose homeostasis is unknown. We show that brain GLP-1 controlled whole-body glucose fate during hyperglycemic conditions. In mice undergoing a hyperglycemic hyperinsulinemic clamp, icv administration of the specific GLP-1 receptor antagonist exendin 9–39 (Ex9) increased muscle glucose utilization and glycogen content. This effect did not require muscle insulin action, as it also occurred in muscle insulin receptor KO mice. Conversely, icv infusion of the GLP-1 receptor agonist exendin 4 (Ex4) reduced insulin-stimulated muscle glucose utilization. In hyperglycemia achieved by i.v. infusion of glucose, icv Ex4, but not Ex9, caused a 4-fold increase in insulin secretion and enhanced liver glycogen storage. However, when glucose was infused intragastrically, icv Ex9 infusion lowered insulin secretion and hepatic glycogen levels, whereas no effects of icv Ex4 were observed. In diabetic mice fed a high-fat diet, a 1-month chronic i.p. Ex9 treatment improved glucose tolerance and fasting glycemia. Our data show that during hyperglycemia, brain GLP-1 inhibited muscle glucose utilization and increased insulin secretion to favor hepatic glycogen stores, preparing efficiently for the next fasting state. PMID:16322793

  11. Brain glucagon-like peptide-1 increases insulin secretion and muscle insulin resistance to favor hepatic glycogen storage.

    PubMed

    Knauf, Claude; Cani, Patrice D; Perrin, Christophe; Iglesias, Miguel A; Maury, Jean François; Bernard, Elodie; Benhamed, Fadilha; Grémeaux, Thierry; Drucker, Daniel J; Kahn, C Ronald; Girard, Jean; Tanti, Jean François; Delzenne, Nathalie M; Postic, Catherine; Burcelin, Rémy

    2005-12-01

    Intestinal glucagon-like peptide-1 (GLP-1) is a hormone released into the hepatoportal circulation that stimulates pancreatic insulin secretion. GLP-1 also acts as a neuropeptide to control food intake and cardiovascular functions, but its neural role in glucose homeostasis is unknown. We show that brain GLP-1 controlled whole-body glucose fate during hyperglycemic conditions. In mice undergoing a hyperglycemic hyperinsulinemic clamp, icv administration of the specific GLP-1 receptor antagonist exendin 9-39 (Ex9) increased muscle glucose utilization and glycogen content. This effect did not require muscle insulin action, as it also occurred in muscle insulin receptor KO mice. Conversely, icv infusion of the GLP-1 receptor agonist exendin 4 (Ex4) reduced insulin-stimulated muscle glucose utilization. In hyperglycemia achieved by i.v. infusion of glucose, icv Ex4, but not Ex9, caused a 4-fold increase in insulin secretion and enhanced liver glycogen storage. However, when glucose was infused intragastrically, icv Ex9 infusion lowered insulin secretion and hepatic glycogen levels, whereas no effects of icv Ex4 were observed. In diabetic mice fed a high-fat diet, a 1-month chronic i.p. Ex9 treatment improved glucose tolerance and fasting glycemia. Our data show that during hyperglycemia, brain GLP-1 inhibited muscle glucose utilization and increased insulin secretion to favor hepatic glycogen stores, preparing efficiently for the next fasting state.

  12. Reduced insulin secretion and glucose intolerance are involved in the fasting susceptibility of common vampire bats.

    PubMed

    Freitas, Mariella B; Queiroz, Joicy F; Dias Gomes, Carolinne I; Collares-Buzato, Carla B; Barbosa, Helena C; Boschero, Antonio C; Gonçalves, Carlos A; Pinheiro, Eliana C

    2013-03-01

    Susceptibility during fasting has been reported for the common vampire bat (Desmodus rotundus), to the point of untimely deaths after only 2-3 nights of fasting. To investigate the underlying physiology of this critical metabolic condition, we analyzed serum insulin levels, pancreatic islets morphometry and immunocytochemistry (ICC), static insulin secretion in pancreas fragments, and insulin signaling mechanism in male vampire bats. A glucose tolerance test (ipGTT) was also performed. Serum insulin was found to be lower in fed vampires compared to other mammals, and was significantly reduced after 24h fasting. Morphometrical analyses revealed small irregular pancreatic islets with reduced percentage of β-cell mass compared to other bats. Static insulin secretion analysis showed that glucose-stimulated insulin secretion was impaired, as insulin levels did not reach significance under high glucose concentrations, whereas the response to the amino acid leucin was preserved. Results from ipGTT showed a failure on glucose clearance, indicating glucose intolerance due to diminished pancreatic insulin secretion and/or decreased β-cell response to glucose. In conclusion, data presented here indicate lower insulinemia and impaired insulin secretion in D. rotundus, which is consistent with the limited ability to store body energy reserves, previously reported in these animals. Whether these metabolic and hormonal features are associated with their blood diet remains to be determined. The peculiar food sharing through blood regurgitation, reported to this species, might be an adaptive mechanism overcoming this metabolic susceptibility.

  13. ER stress in adipocytes inhibits insulin signaling, represses lipolysis, and alters the secretion of adipokines without inhibiting glucose transport.

    PubMed

    Xu, L; Spinas, G A; Niessen, M

    2010-08-01

    The endoplasmic reticulum (ER) is the intra-cellular site, where secreted and membrane proteins are synthesized. ER stress and activation of the unfolded protein response (UPR) contribute to insulin resistance and the development of diabetes in obesity. It was shown previously in hepatocytes that the UPR activates c-jun N-terminal kinase (JNK), which phosphorylates insulin receptor substrate (IRS) proteins on serine residues thereby inhibiting insulin signal transduction. Here we describe how ER stress affects insulin signaling and the biological function of adipocytes. In addition to inhibition of IRS we found that ER stress downregulates the expression of the insulin receptor. Concomitantly, insulin-induced activation of Akt/PKB and of ERK1/2 was strongly inhibited. Ectopic expression of IRS1 or IRS2 strongly counteracted the inhibitory effect of ER stress on insulin signaling while pharmacological inhibition of JNK with SP600125 resulted only in a mild improvement. ER stress decreased the secretion of the adipokines adiponectin and leptin, but strongly increased secretion of IL-6. ER stress inhibited expression and insulin-induced phosphorylation of AS160, reduced lipolysis but did not inhibit glucose transport. Finally, supernatants collected from 3T3-L1 adipocytes undergoing ER stress improved or impaired proliferation when used to condition the culture medium of INS-1E beta-cells dependent on the degree of ER stress. It appears that ER stress in adipocytes might initially lead to changes resembling early prediabetic stages, which at least in part support the regulation of systemic energy homeostasis. Copyright Georg Thieme Verlag KG Stuttgart New York.

  14. [Effects of chemical constituents of Crossostephium chinense on insulin secretion in rat islets in vitro].

    PubMed

    Zou, Lei; Wu, Qi; Yang, Xiuwei; Fu, Dexian

    2009-06-01

    To investigate the effects of the chemical constituents of the whole herbs of Crossostephium chinense on insulin secretion in rat islets. Islets were isolated from rat pancreata, cultured in vitro, and measured by color signals of dithizone stained digestion solution for detection of pancreatic islets. The morphological observation of islets was carried out by inverted microscope. The effects of test compounds, scopoletin (1), scopolin (2), tanacetin (3), quercetagetin-3,6,7-trimethylether (4) and 5-O-methyl-myo-inositol (5) isolated from the whole herbs of C. chinense, on the insulin secreting level from islets were compared with those of glybenclamide as a positive control substances, and the difference in insulin secreting level from islets between the presence and absence of test compounds was assayed. There was no difference in basal insulin secretion before and after 2 h incubation period of rat islets. The islets treated with quercetagetin-3,6,7-trimethylether have about 2-fold higher insulin secreting level (P < 0.01) compared a normal control group. The islets treated with 5-O-methyl-myo-inositol have about 1.5-fold higher insulin secreting level (P < 0.05) compared to a normal control group. Whereas the islets treated with scopoletin show about 1.9-fold lower basal insulin secreting level (P < 0.05) than a normal control group. In this paper the developed cultivation method of isolated pancreatic islets from rat can be used as a kind of islet-based drug screening model for diabetes mellitus in vitro. Quercetagetin-3,6,7-trimethylether and 5-O-methyl-myo-inositol could enhance rat islet insulin secretion and further in vivo studies are needed to clarify the nature of such an observation. However, scopletin suppress rat islet insulin secretion.

  15. Angiotensin II induces differential insulin action in rat skeletal muscle.

    PubMed

    Surapongchai, Juthamard; Prasannarong, Mujalin; Bupha-Intr, Tepmanas; Saengsirisuwan, Vitoon

    2017-03-01

    Angiotensin II (ANGII) is reportedly involved in the development of skeletal muscle insulin resistance. The present investigation evaluated the effects of two ANGII doses on the phenotypic characteristics of insulin resistance syndrome and insulin action and signaling in rat skeletal muscle. Male Sprague-Dawley rats were infused with either saline (SHAM) or ANGII at a commonly used pressor dose (100 ng/kg/min; ANGII-100) or a higher pressor dose (500 ng/kg/min; ANGII-500) via osmotic minipumps for 14 days. We demonstrated that ANGII-100-infused rats exhibited the phenotypic features of non-obese insulin resistance syndrome, including hypertension, impaired glucose tolerance and insulin resistance of glucose uptake in the soleus muscle, whereas ANGII-500-treated rats exhibited diabetes-like symptoms, such as post-prandial hyperglycemia, impaired insulin secretion and hypertriglyceridemia. At the cellular level, insulin-stimulated glucose uptake in the soleus muscle of the ANGII-100 group was 33% lower (P < 0.05) than that in the SHAM group and was associated with increased insulin-stimulated IRS-1 Ser(307) and decreased Akt Ser(473) and AS160 Thr(642) phosphorylation and GLUT-4 expression. However, ANGII-500 infusion did not induce skeletal muscle insulin resistance or impair insulin signaling elements as initially anticipated. Moreover, we found that insulin-stimulated glucose uptake in the ANGII-500 group was accompanied by the enhanced expression of ACE2 and MasR proteins, which are the key elements in the non-classical pathway of the renin-angiotensin system. Collectively, this study demonstrates for the first time that chronic infusion with these two pressor doses of ANGII induced differential metabolic responses at both the systemic and skeletal muscle levels. © 2017 Society for Endocrinology.

  16. Association of nocturnal melatonin secretion with insulin resistance in nondiabetic young women.

    PubMed

    McMullan, Ciaran J; Curhan, Gary C; Schernhammer, Eva S; Forman, John P

    2013-07-15

    Exogenous melatonin ameliorates insulin resistance in animals, while among humans, polymorphisms in the melatonin receptor gene are associated with insulin resistance. We aimed to investigate the association of endogenous nocturnal melatonin secretion with insulin resistance in humans. We analyzed the association between endogenous nocturnal melatonin secretion, estimated by measuring the main melatonin metabolite, 6-sulfatoxymelatonin, from the first morning urinary void, and the prevalence of insulin resistance based on fasting blood samples collected in a cross-sectional study of 1,075 US women (1997-1999) without diabetes, hypertension, or malignancy. Urinary 6-sulfatoxymelatonin level was standardized to urinary creatinine level; insulin resistance was defined as an insulin sensitivity index value (using the McAuley formula) less than 7.85. Logistic regression models included adjustment for age, body mass index, smoking, physical activity, alcohol intake, dietary glycemic index, family history of diabetes mellitus, blood pressure, plasma total cholesterol, uric acid, and estimated glomerular filtration rate. Higher nocturnal melatonin secretion was inversely associated with insulin levels and insulin resistance. In fully adjusted models, the odds ratio for insulin resistance was 0.45 (95% confidence interval: 0.28, 0.74) among women in the highest quartile of urinary 6-sulfatoxymelatonin:creatinine ratio compared with women in the lowest quartile. Nocturnal melatonin secretion is independently and inversely associated with insulin resistance.

  17. Chronic exposure to free fatty acid reduces pancreatic beta cell insulin content by increasing basal insulin secretion that is not compensated for by a corresponding increase in proinsulin biosynthesis translation.

    PubMed Central

    Bollheimer, L C; Skelly, R H; Chester, M W; McGarry, J D; Rhodes, C J

    1998-01-01

    The pancreatic beta cell normally maintains a stable balance among insulin secretion, insulin production, and insulin degradation to keep optimal intracellular stores of the hormone. Elevated levels of FFA markedly enhance insulin secretion; however, the effects of FFA on insulin production and intracellular stores remain unclear. In this study, twofold elevation in total circulating FFA effected by infusion of lard oil and heparin into rats for 6 h under normoglycemic conditions resulted in a marked elevation of circulating insulin levels evident after 4 h, and a 30% decrease in pancreatic insulin content after a 6-h infusion in vivo. Adding 125 muM oleate to isolated rat pancreatic islets cultured with 5.6 mM glucose caused a 50% fall in their insulin content over 24 h, coupled with a marked enhancement of basal insulin secretion. Both effects of fatty acid were blocked by somatostatin. In contrast to the stimulatory effects of oleate on insulin secretion, glucose-induced proinsulin biosynthesis was inhibited by oleate up to 24 h, but was unaffected thereafter. This result was in spite of a two- to threefold oleate-induced increase in preproinsulin mRNA levels, underscoring the importance of translational regulation of proinsulin biosynthesis in maintaining beta cell insulin stores. Collectively, these results suggest that chronically elevated FFA contribute to beta cell dysfunction in the pathogenesis of NIDDM by significantly increasing the basal rate of insulin secretion. This increase in turn results in a decrease in the beta cell's intracellular stores that cannot be offset by commensurate FFA induction of proinsulin biosynthesis. PMID:9486980

  18. Effects of sodium tungstate on insulin and glucagon secretion in the perfused rat pancreas.

    PubMed

    Rodríguez-Gallardo, J; Silvestre, R A; Egido, E M; Marco, J

    2000-08-18

    Both the direct effect of sodium tungstate on insulin and glucagon secretion in the perfused rat pancreas, and the insulin response to glucose and arginine in pancreases isolated from tungstate-pretreated rats were studied. Infusion of tungstate stimulated insulin output in a dose-dependent manner. The insulinotropic effect of tungstate was observed at normal (5.5 mM), and moderately high (9 mM) glucose concentrations, but not at a low glucose concentration (3.2 mM). Tungstate-induced insulin output was blocked by diazoxide, somatostatin, and amylin, suggesting several targets for tungstate at the B-cell secretory machinery. Glucagon release was not modified by tungstate. Pancreases from chronically tungstate-treated rats showed an enhanced response to glucose but not to arginine. Our results indicate that the reported reduction of glycemia caused by tungstate administration is, at least in part, due to its direct insulinotropic activity. Furthermore, chronic tungstate treatment may prime the B-cell, leading to over-response to a glucose stimulus.

  19. Dopamine D2-like receptors are expressed in pancreatic beta cells and mediate inhibition of insulin secretion.

    PubMed

    Rubí, Blanca; Ljubicic, Sanda; Pournourmohammadi, Shirin; Carobbio, Stefania; Armanet, Mathieu; Bartley, Clarissa; Maechler, Pierre

    2005-11-04

    Dopamine signaling is mediated by five cloned receptors, grouped into D1-like (D1 and D5) and D2-like (D2, D3 and D4) families. We identified by reverse transcription-PCR the presence of dopamine receptors from both families in INS-1E insulin-secreting cells as well as in rodent and human isolated islets. D2 receptor expression was confirmed by immunodetection revealing localization on insulin secretory granules of INS-1E and primary rodent and human beta cells. We then tested potential effects mediated by the identified receptors on beta cell function. Dopamine (10 microM) and the D2-like receptor agonist quinpirole (5 microM) inhibited glucose-stimulated insulin secretion tested in several models, i.e. INS-1E beta cells, fluorescence-activated cell-sorted primary rat beta cells, and pancreatic islets of rat, mouse, and human origin. Insulin exocytosis is controlled by metabolism coupled to cytosolic calcium changes. Measurements of glucose-induced mitochondrial hyperpolarization and ATP generation showed that dopamine and D2-like agonists did not inhibit glucose metabolism. On the other hand, dopamine decreased cell membrane depolarization as well as cytosolic calcium increases evoked by glucose stimulation in INS-1E beta cells. These results show for the first time that dopamine receptors are expressed in pancreatic beta cells. Dopamine inhibited glucose-stimulated insulin secretion, an effect that could be ascribed to D2-like receptors. Regarding the molecular mechanisms implicated in dopamine-mediated inhibition of insulin release, our results point to distal steps in metabolism-secretion coupling. Thus, the role played by dopamine in glucose homeostasis might involve dopamine receptors, expressed in pancreatic beta cells, modulating insulin release.

  20. Enhanced insulin secretion responsiveness and islet adrenergic desensitization after chronic norepinephrine suppression is discontinued in fetal sheep

    PubMed Central

    Chen, Xiaochuan; Green, Alice S.; Macko, Antoni R.; Yates, Dustin T.; Kelly, Amy C.

    2013-01-01

    Intrauterine growth-restricted (IUGR) fetuses experience prolonged hypoxemia, hypoglycemia, and elevated norepinephrine (NE) concentrations, resulting in hypoinsulinemia and β-cell dysfunction. Previously, we showed that acute adrenergic blockade revealed enhanced insulin secretion responsiveness in the IUGR fetus. To determine whether chronic exposure to NE alone enhances β-cell responsiveness afterward, we continuously infused NE into fetal sheep for 7 days and, after terminating the infusion, evaluated glucose-stimulated insulin secretion (GSIS) and glucose-potentiated arginine-induced insulin secretion (GPAIS). During treatment, NE-infused fetuses had greater (P < 0.05) plasma NE concentrations and exhibited hyperglycemia (P < 0.01) and hypoinsulinemia (P < 0.01) compared with controls. GSIS during the NE infusion was also reduced (P < 0.05) compared with pretreatment values. GSIS and GPAIS were approximately fourfold greater (P < 0.01) in NE fetuses 3 h after the 7 days that NE infusion was discontinued compared with age-matched controls or pretreatment GSIS and GPAIS values of NE fetuses. In isolated pancreatic islets from NE fetuses, mRNA concentrations of adrenergic receptor isoforms (α1D, α2A, α2C, and β1), G protein subunit-αi-2, and uncoupling protein 2 were lower (P < 0.05) compared with controls, but β-cell regulatory genes were not different. Our findings indicate that chronic exposure to elevated NE persistently suppresses insulin secretion. After removal, NE fetuses demonstrated a compensatory enhancement in insulin secretion that was associated with adrenergic desensitization and greater stimulus-secretion coupling in pancreatic islets. PMID:24253046

  1. New type 2 diabetes risk genes provide new insights in insulin secretion mechanisms.

    PubMed

    Schäfer, Silke A; Machicao, Fausto; Fritsche, Andreas; Häring, Hans-Ulrich; Kantartzis, Konstantinos

    2011-08-01

    Type 2 diabetes results from the inability of beta cells to increase insulin secretion sufficiently to compensate for insulin resistance. Insulin resistance is thought to result mainly from environmental factors, such as obesity. However, there is compelling evidence that the decline of both insulin sensitivity and insulin secretion have also a genetic component. Recent genome-wide association studies identified several novel risk genes for type 2 diabetes. The vast majority of these genes affect beta cell function by molecular mechanisms that remain unknown in detail. Nevertheless, we and others could show that a group of genes affect glucose-stimulated insulin secretion, a group incretin-stimulated insulin secretion (incretin sensitivity or secretion) and a group proinsulin-to-insulin conversion. The most important so far type 2 diabetes risk gene, TCF7L2, interferes with all three mechanisms. In addition to advancing knowledge in the pathophysiology of type 2 diabetes, the discovery of novel genetic determinants of diabetes susceptibility may help understanding of gene-environment, gene-therapy and gene-gene interactions. It was also hoped that it could make determination of the individual risk for type 2 diabetes feasible. However, the allelic relative risks of most genetic variants discovered so far are relatively low. Thus, at present, clinical criteria assess the risk for type 2 diabetes with greater sensitivity and specificity than the combination of all known genetic variants.

  2. Plasma HDL-cholesterol and triglycerides, but not LDL-cholesterol, are associated with insulin secretion in non-diabetic subjects.

    PubMed

    Natali, Andrea; Baldi, Simona; Bonnet, Fabrice; Petrie, John; Trifirò, Silvia; Tricò, Domenico; Mari, Andrea

    2017-04-01

    Experimental data support the notion that lipoproteins might directly affect beta cell function, however clinical data are sparse and inconsistent. We aimed at verifying whether, independently of major confounders, serum lipids are associated with alterations in insulin secretion or clearance non-diabetic subjects. Cross sectional and observational prospective (3.5yrs), multicentre study in which 1016 non-diabetic volunteers aged 30-60yrs. and with a wide range of BMI (20.0-39.9kg/m(2)) were recruited in a setting of University hospital ambulatory care (RISC study). baseline fasting lipids, fasting and OGTT-induced insulin secretion and clearance (measured by glucose and C-peptide modeling), peripheral insulin sensitivity (by the euglycemic clamp). Lipids and OGTT were repeated in 980 subjects after 3.5years. LDL-cholesterol did not show independent associations with fasting or stimulated insulin secretion or clearance. After accounting for potential confounders, HDL-cholesterol displayed negative and triglycerides positive independent associations with fasting and OGTT insulin secretion; neither with insulin clearance. Low HDL-cholesterol and high triglycerides were associated with an increase in glucose-dependent and a decrease in non-glucose-dependent insulin secretion. Over 3.5years both an HDL-cholesterol decline and a triglycerides rise were associated with an increase in fasting insulin secretion independent of changes in body weight or plasma glucose. LDL-cholesterol does not seem to influence any major determinant of insulin bioavailability while low HDL-cholesterol and high triglycerides might contribute to sustain the abnormalities in insulin secretion that characterize the pre-diabetic state. Copyright © 2017 Elsevier Inc. All rights reserved.

  3. α/β-Hydrolase domain-6 and saturated long chain monoacylglycerol regulate insulin secretion promoted by both fuel and non-fuel stimuli.

    PubMed

    Zhao, Shangang; Poursharifi, Pegah; Mugabo, Yves; Levens, Emily J; Vivot, Kevin; Attane, Camille; Iglesias, Jose; Peyot, Marie-Line; Joly, Erik; Madiraju, S R Murthy; Prentki, Marc

    2015-12-01

    α/β-Hydrolase domain-6 (ABHD6) is a newly identified monoacylglycerol (MAG) lipase. We recently reported that it negatively regulates glucose stimulated insulin secretion (GSIS) in the β cells by hydrolyzing lipolysis-derived MAG that acts as a metabolic coupling factor and signaling molecule via exocytotic regulator Munc13-1. Whether ABHD6 and MAG play a role in response to all classes of insulin secretagogues, in particular various fuel and non-fuel stimuli, is unknown. Insulin secretion in response to various classes of secretagogues, exogenous MAG and pharmacological agents was measured in islets of mice deficient in ABHD6 specifically in the β cell (BKO). Islet perifusion experiments and determinations of glucose and fatty acid metabolism, cytosolic Ca(2+) and MAG species levels were carried out. Deletion of ABHD6 potentiated insulin secretion in response to the fuels glutamine plus leucine and α-ketoisocaproate and to the non-fuel stimuli glucagon-like peptide 1, carbamylcholine and elevated KCl. Fatty acids amplified GSIS in control and BKO mice to the same extent. Exogenous 1-MAG amplified insulin secretion in response to fuel and non-fuel stimuli. MAG hydrolysis activity was greatly reduced in BKO islets without changes in total diacylglycerol and triacylglycerol lipase activity. ABHD6 deletion induced insulin secretion independently from KATP channels and did not alter the glucose induced rise in intracellular Ca(2+). Perifusion studies showed elevated insulin secretion during second phase of GSIS in BKO islets that was not due to altered cytosolic Ca(2+) signaling or because of changes in glucose and fatty acid metabolism. Glucose increased islet saturated long chain 1-MAG species and ABHD6 deletion caused accumulation of these 1-MAG species at both low and elevated glucose. ABHD6 regulates insulin secretion in response to fuel stimuli at large and some non-fuel stimuli by controlling long chain saturated 1-MAG levels that synergize with other

  4. Free fatty acid receptor 1 (FFAR1/GPR40) signaling affects insulin secretion by enhancing mitochondrial respiration during palmitate exposure.

    PubMed

    Kristinsson, Hjalti; Bergsten, Peter; Sargsyan, Ernest

    2015-12-01

    Fatty acids affect insulin secretion via metabolism and FFAR1-mediated signaling. Recent reports indicate that these two pathways act synergistically. Still it remains unclear how they interrelate. Taking into account the key role of mitochondria in insulin secretion, we attempted to dissect the metabolic and FFAR1-mediated effects of fatty acids on mitochondrial function. One-hour culture of MIN6 cells with palmitate significantly enhanced mitochondrial respiration. Antagonism or silencing of FFAR1 prevented the palmitate-induced rise in respiration. On the other hand, in the absence of extracellular palmitate FFAR1 agonists caused a modest increase in respiration. Using an agonist of the M3 muscarinic acetylcholine receptor and PKC inhibitor we found that in the presence of the fatty acid mitochondrial respiration is regulated via Gαq protein-coupled receptor signaling. The increase in respiration in palmitate-treated cells was largely due to increased glucose utilization and oxidation. However, glucose utilization was not dependent on FFAR1 signaling. Collectively, these results indicate that mitochondrial respiration in palmitate-treated cells is enhanced via combined action of intracellular metabolism of the fatty acid and the Gαq-coupled FFAR1 signaling. Long-term palmitate exposure reduced ATP-coupling efficiency of mitochondria and deteriorated insulin secretion. The presence of the FFAR1 antagonist during culture did not improve ATP-coupling efficiency, however, it resulted in enhanced mitochondrial respiration and improved insulin secretion after culture. Taken together, our study demonstrates that during palmitate exposure, integrated actions of fatty acid metabolism and fatty acid-induced FFAR1 signaling on mitochondrial respiration underlie the synergistic action of the two pathways on insulin secretion.

  5. Pancreatic insulin secretion in rats fed a soy protein high fat diet depends on the interaction between the amino acid pattern and isoflavones.

    PubMed

    Noriega-López, Lilia; Tovar, Armando R; Gonzalez-Granillo, Marcela; Hernández-Pando, Rogelio; Escalante, Bruno; Santillán-Doherty, Patricio; Torres, Nimbe

    2007-07-13

    Obesity is frequently associated with the consumption of high carbohydrate/fat diets leading to hyperinsulinemia. We have demonstrated that soy protein (SP) reduces hyperinsulinemia, but it is unclear by which mechanism. Thus, the purpose of the present work was to establish whether SP stimulates insulin secretion to a lower extent and/or reduces insulin resistance, and to understand its molecular mechanism of action in pancreatic islets of rats with diet-induced obesity. Long-term consumption of SP in a high fat (HF) diet significantly decreased serum glucose, free fatty acids, leptin, and the insulin:glucagon ratio compared with animals fed a casein HF diet. Hyperglycemic clamps indicated that SP stimulated insulin secretion to a lower extent despite HF consumption. Furthermore, there was lower pancreatic islet area and insulin, SREBP-1, PPARgamma, and GLUT-2 mRNA abundance in comparison with rats fed the casein HF diet. Euglycemic-hyperinsulinemic clamps showed that the SP diet prevented insulin resistance despite consumption of a HF diet. Incubation of pancreatic islets with isoflavones reduced insulin secretion and expression of PPARgamma. Addition of amino acids resembling the plasma concentration of rats fed casein stimulated insulin secretion; a response that was reduced by the presence of isoflavones, whereas the amino acid pattern resembling the plasma concentration of rats fed SP barely stimulated insulin release. Infusion of isoflavones during the hyperglycemic clamps did not stimulate insulin secretion. Therefore, isoflavones as well as the amino acid pattern seen after SP consumption stimulated insulin secretion to a lower extent, decreasing PPARgamma, GLUT-2, and SREBP-1 expression, and ameliorating hyperinsulinemia observed during obesity.

  6. Evaluation of immunoisolated insulin-secreting beta TC6-F7 cells as a bioartificial pancreas.

    PubMed

    Mamujee, S N; Zhou, D; Wheeler, M B; Vacek, I; Sun, A M

    1997-01-01

    To evaluate the growth and insulin secretion from microencapsulated beta TC6-F7 cells in vitro and to assess the in vivo function of microencapsulated cells transplanted in rats with steptozotocin (STZ)-induced diabetes. Alginate-poly-L-lysine encapsulated beta TC6-F7 cells were exposed to glucose, isobutylmethylxanthine (IBMX) and glucagon-like peptide I (7-36 amide) in a static in vitro challenge. In vivo, 2.5-3.5 x 10(7) encapsulated cells were implanted into diabetic rats. Graft function was evaluated by monitoring blood glucose concentrations and by an intraperitoneal glucose tolerance test. The cell density (number of cells per capsule) of cultured microencapsulated beta TC6-F7 cells increased almost 35-fold over a 55 day observation period to reach a plateau of approximately 3500 cells/capsule. While insulin secretion per capsule remained unchanged over the first 21 days of culture, a 7-fold increase was observed during the last 14 days of the 55 day observation period. Intraperitoneal transplantation of 3.5 x 10(7) encapsulated cells into diabetic rats resulted, within 24 hours, in reversal of hyperglycemia for up to 60 days. Post-transplantation blood glucose concentrations varied between 2 and 4 mM. Glucose clearance rates evaluated by an intraperitoneal glucose tolerance test at 30 days post-transplantation resulted in a markedly flat glucose clearance curve with blood glucose never rising above 4 mM. The glucose challenge of microencapsulated cells recovered 30 days post-transplantation resulted in a 2-fold increase in insulin response at glucose concentrations greater than 5.5 mM as compared to glucose-free media. In addition, immunostaining of recovered grafted tissue for insulin, reveals a strong presence of the peptide within the cell population. These data demonstrate the potential use of an immunoisolated beta-cell line for the treatment of diabetes.

  7. Effect of Human Myotubes-Derived Media on Glucose-Stimulated Insulin Secretion

    PubMed Central

    Cataldo, Luis R.; Gutierrez, Juan; Santos, José L.; Casas, Mariana; Contreras-Ferrat, Ariel E.; Moro, Cedric; Bouzakri, Karim

    2017-01-01

    Fasting to postprandial transition requires a tight adjustment of insulin secretion to its demand, so tissue (e.g., skeletal muscle) glucose supply is assured while hypo-/hyperglycemia are prevented. High muscle glucose disposal after meals is pivotal for adapting to increased glycemia and might drive insulin secretion through muscle-released factors (e.g., myokines). We hypothesized that insulin influences myokine secretion and then increases glucose-stimulated insulin secretion (GSIS). In conditioned media from human myotubes incubated with/without insulin (100 nmol/L) for 24 h, myokines were qualitatively and quantitatively characterized using an antibody-based array and ELISA-based technology, respectively. C57BL6/J mice islets and Wistar rat beta cells were incubated for 24 h with control and conditioned media from noninsulin- and insulin-treated myotubes prior to GSIS determination. Conditioned media from insulin-treated versus nontreated myotubes had higher RANTES but lower IL6, IL8, and MCP1 concentration. Qualitative analyses revealed that conditioned media from noninsulin- and insulin-treated myotubes expressed 32 and 23 out of 80 myokines, respectively. Islets incubated with conditioned media from noninsulin-treated myotubes had higher GSIS versus control islets (p < 0.05). Meanwhile, conditioned media from insulin-treated myotubes did not influence GSIS. In beta cells, GSIS was similar across conditions. In conclusion, factors being present in noninsulin-stimulated muscle cell-derived media appear to influence GSIS in mice islets. PMID:28286777

  8. Effect of Human Myotubes-Derived Media on Glucose-Stimulated Insulin Secretion.

    PubMed

    Mizgier, Maria L; Cataldo, Luis R; Gutierrez, Juan; Santos, José L; Casas, Mariana; Llanos, Paola; Contreras-Ferrat, Ariel E; Moro, Cedric; Bouzakri, Karim; Galgani, Jose E

    2017-01-01

    Fasting to postprandial transition requires a tight adjustment of insulin secretion to its demand, so tissue (e.g., skeletal muscle) glucose supply is assured while hypo-/hyperglycemia are prevented. High muscle glucose disposal after meals is pivotal for adapting to increased glycemia and might drive insulin secretion through muscle-released factors (e.g., myokines). We hypothesized that insulin influences myokine secretion and then increases glucose-stimulated insulin secretion (GSIS). In conditioned media from human myotubes incubated with/without insulin (100 nmol/L) for 24 h, myokines were qualitatively and quantitatively characterized using an antibody-based array and ELISA-based technology, respectively. C57BL6/J mice islets and Wistar rat beta cells were incubated for 24 h with control and conditioned media from noninsulin- and insulin-treated myotubes prior to GSIS determination. Conditioned media from insulin-treated versus nontreated myotubes had higher RANTES but lower IL6, IL8, and MCP1 concentration. Qualitative analyses revealed that conditioned media from noninsulin- and insulin-treated myotubes expressed 32 and 23 out of 80 myokines, respectively. Islets incubated with conditioned media from noninsulin-treated myotubes had higher GSIS versus control islets (p < 0.05). Meanwhile, conditioned media from insulin-treated myotubes did not influence GSIS. In beta cells, GSIS was similar across conditions. In conclusion, factors being present in noninsulin-stimulated muscle cell-derived media appear to influence GSIS in mice islets.

  9. Regulation of Endogenous (Male) Rodent GLP-1 Secretion and Human Islet Insulin Secretion by Antagonism of Somatostatin Receptor 5.

    PubMed

    Farb, Thomas B; Adeva, Marta; Beauchamp, Thomas J; Cabrera, Over; Coates, David A; DeShea Meredith, Tamika; Droz, Brian A; Efanov, Alexander; Ficorilli, James V; Gackenheimer, Susan L; Martinez-Grau, Maria A; Molero, Victoriano; Ruano, Gema; Statnick, Michael A; Suter, Todd M; Syed, Samreen K; Toledo, Miguel A; Willard, Francis S; Zhou, Xin; Bokvist, Krister B; Barrett, David G

    2017-09-11

    Incretin and insulin responses to nutrient loads are suppressed in persons with diabetes, resulting in decreased glycemic control. Whereas agents including sulfonylureas and Dipeptidyl peptidase-4 inhibitors (DPP4i) partially reverse these effects and provide therapeutic benefit, their modes of action limit efficacy. Because somatostatin (SST) has been shown to suppress both insulin and GLP-1 secretion through the Gi-coupled SST receptor 5 (SSTR5) isoform in vitro, antagonism of SSTR5 may improve glycemic control via intervention in both pathways. Here we show that a novel potent and selective SSTR5 antagonist reverses the blunting effects of SST on insulin secretion from isolated human islets, and demonstrate for the first time that SSTR5 antagonism affords increased levels of systemic GLP-1 in vivo. Knocking out Sstr5 in mice provided a similar increase in systemic GLP-1 levels, which were not increased further by treatment with the antagonist. Treatment of mice with the SSTR5 antagonist in combination with a DPP4i afforded increases in systemic GLP-1 levels that were more than additive, and resulted in greater glycemic control compared to either agent alone. In isolated human islets, the SSTR5 antagonist completely reversed the inhibitory effect of exogenous SST-14 on insulin secretion. Taken together, these data suggest that SSTR5 antagonism should increase circulating GLP-1 levels and stimulate insulin secretion (directly and via GLP-1) in humans, improving glycemic control in patients with diabetes. Copyright © 2017 Endocrine Society.

  10. Enterovirus infection of human islets of Langerhans affects β-cell function resulting in disintegrated islets, decreased glucose stimulated insulin secretion and loss of Golgi structure.

    PubMed

    Hodik, M; Skog, O; Lukinius, A; Isaza-Correa, J M; Kuipers, J; Giepmans, B N G; Frisk, G

    2016-01-01

    In type 1 diabetes (T1D), most insulin-producing β cells are destroyed, but the trigger is unknown. One of the possible triggers is a virus infection and the aim of this study was to test if enterovirus infection affects glucose stimulated insulin secretion and the effect of virus replication on cellular macromolecules and organelles involved in insulin secretion. Isolated human islets were infected with different strains of coxsackievirus B (CVB) virus and the glucose-stimulated insulin release (GSIS) was measured in a dynamic perifusion system. Classical morphological electron microscopy, large-scale electron microscopy, so-called nanotomy, and immunohistochemistry were used to study to what extent virus-infected β cells contained insulin, and real-time PCR was used to analyze virus induced changes of islet specific genes. In islets infected with CVB, GSIS was reduced in correlation with the degree of virus-induced islet disintegration. The expression of the gene encoding insulin was decreased in infected islets, whereas the expression of glucagon was not affected. Also, in islets that were somewhat disintegrated, there were uninfected β cells. Ultrastructural analysis revealed that virus particles and virus replication complexes were only present in β cells. There was a significant number of insulin granules remaining in the virus-infected β cells, despite decreased expression of insulin mRNA. In addition, no typical Golgi apparatus was detected in these cells. Exposure of islets to synthetic dsRNA potentiated glucose-stimulated insulin secretion. Glucose-stimulated insulin secretion; organelles involved in insulin secretion and gene expression were all affected by CVB replication in β cells.

  11. Enterovirus infection of human islets of Langerhans affects β-cell function resulting in disintegrated islets, decreased glucose stimulated insulin secretion and loss of Golgi structure

    PubMed Central

    Hodik, M; Skog, O; Lukinius, A; Isaza-Correa, J M; Kuipers, J; Giepmans, B N G; Frisk, G

    2016-01-01

    Aims/hypothesis In type 1 diabetes (T1D), most insulin-producing β cells are destroyed, but the trigger is unknown. One of the possible triggers is a virus infection and the aim of this study was to test if enterovirus infection affects glucose stimulated insulin secretion and the effect of virus replication on cellular macromolecules and organelles involved in insulin secretion. Methods Isolated human islets were infected with different strains of coxsackievirus B (CVB) virus and the glucose-stimulated insulin release (GSIS) was measured in a dynamic perifusion system. Classical morphological electron microscopy, large-scale electron microscopy, so-called nanotomy, and immunohistochemistry were used to study to what extent virus-infected β cells contained insulin, and real-time PCR was used to analyze virus induced changes of islet specific genes. Results In islets infected with CVB, GSIS was reduced in correlation with the degree of virus-induced islet disintegration. The expression of the gene encoding insulin was decreased in infected islets, whereas the expression of glucagon was not affected. Also, in islets that were somewhat disintegrated, there were uninfected β cells. Ultrastructural analysis revealed that virus particles and virus replication complexes were only present in β cells. There was a significant number of insulin granules remaining in the virus-infected β cells, despite decreased expression of insulin mRNA. In addition, no typical Golgi apparatus was detected in these cells. Exposure of islets to synthetic dsRNA potentiated glucose-stimulated insulin secretion. Conclusions/interpretation Glucose-stimulated insulin secretion; organelles involved in insulin secretion and gene expression were all affected by CVB replication in β cells. PMID:27547409

  12. Glucose-regulated and drug-perturbed phosphoproteome reveals molecular mechanisms controlling insulin secretion

    PubMed Central

    Sacco, Francesca; Humphrey, Sean J.; Cox, Jürgen; Mischnik, Marcel; Schulte, Anke; Klabunde, Thomas; Schäfer, Matthias; Mann, Matthias

    2016-01-01

    Insulin-secreting beta cells play an essential role in maintaining physiological blood glucose levels, and their dysfunction leads to the development of diabetes. To elucidate the signalling events regulating insulin secretion, we applied a recently developed phosphoproteomics workflow. We quantified the time-resolved phosphoproteome of murine pancreatic cells following their exposure to glucose and in combination with small molecule compounds that promote insulin secretion. The quantitative phosphoproteome of 30,000 sites clustered into three main groups in concordance with the modulation of the three key kinases: PKA, PKC and CK2A. A high-resolution time course revealed key novel regulatory sites, revealing the importance of methyltransferase DNMT3A phosphorylation in the glucose response. Remarkably a significant proportion of these novel regulatory sites is significantly downregulated in diabetic islets. Control of insulin secretion is embedded in an unexpectedly broad and complex range of cellular functions, which are perturbed by drugs in multiple ways. PMID:27841257

  13. Identifying the Targets of the Amplifying Pathway for Insulin Secretion in Pancreatic β-Cells by Kinetic Modeling of Granule Exocytosis

    PubMed Central

    Chen, Yi-der; Wang, Shaokun; Sherman, Arthur

    2008-01-01

    A kinetic model for insulin secretion in pancreatic β-cells is adapted from a model for fast exocytosis in chromaffin cells. The fusion of primed granules with the plasma membrane is assumed to occur only in the “microdomain” near voltage-sensitive L-type Ca2+-channels, where [Ca2+] can reach micromolar levels. In contrast, resupply and priming of granules are assumed to depend on the cytosolic [Ca2+]. Adding a two-compartment model to handle the temporal distribution of Ca2+ between the microdomain and the cytosol, we obtain a unified model that can generate both the fast granule fusion and the slow insulin secretion found experimentally in response to a step of membrane potential. The model can simulate the potentiation induced in islets by preincubation with glucose and the reduction in second-phase insulin secretion induced by blocking R-type Ca2+-channels (CaV2.3). The model indicates that increased second-phase insulin secretion induced by the amplifying signal is controlled by the “resupply” step of the exocytosis cascade. In contrast, enhancement of priming is a good candidate for amplification of first-phase secretion by glucose, cyclic adenosine 3′:5′-cyclic monophosphate, and protein kinase C. Finally, insulin secretion is enhanced when the amplifying signal oscillates in phase with the triggering Ca2+-signal. PMID:18515381

  14. Differential stimulation of insulin secretion by GLP-1 and Kisspeptin-10.

    PubMed

    Schwetz, Tara A; Reissaus, Christopher A; Piston, David W

    2014-01-01

    β-cells in the pancreatic islet respond to elevated plasma glucose by secreting insulin to maintain glucose homeostasis. In addition to glucose stimulation, insulin secretion is modulated by numerous G-protein coupled receptors (GPCRs). The GPCR ligands Kisspeptin-10 (KP) and glucagon-like peptide-1 (GLP-1) potentiate insulin secretion through Gq and Gs-coupled receptors, respectively. Despite many studies, the signaling mechanisms by which KP and GLP-1 potentiate insulin release are not thoroughly understood. We investigated the downstream signaling pathways of these ligands and their affects on cellular redox potential, intracellular calcium activity ([Ca(2+)]i), and insulin secretion from β-cells within intact murine islets. In contrast to previous studies performed on single β-cells, neither KP nor GLP-1 affect [Ca(2+)]i upon stimulation with glucose. KP significantly increases the cellular redox potential, while no effect is observed with GLP-1, suggesting that KP and GLP-1 potentiate insulin secretion through different mechanisms. Co-treatment with KP and the Gβγ-subunit inhibitor gallein inhibits insulin secretion similar to that observed with gallein alone, while co-treatment with gallein and GLP-1 does not differ from GLP-1 alone. In contrast, co-treatment with the Gβγ activator mSIRK and either KP or GLP-1 stimulates insulin release similar to mSIRK alone. Neither gallein nor mSIRK alter [Ca(2+)]i activity in the presence of KP or GLP-1. These data suggest that KP likely alters insulin secretion through a Gβγ-dependent process that stimulates glucose metabolism without altering Ca(2+) activity, while GLP-1 does so, at least partly, through a Gα-dependent pathway that is independent of both metabolism and Ca(2+).

  15. Differential Stimulation of Insulin Secretion by GLP-1 and Kisspeptin-10

    PubMed Central

    Schwetz, Tara A.; Reissaus, Christopher A.; Piston, David W.

    2014-01-01

    β-cells in the pancreatic islet respond to elevated plasma glucose by secreting insulin to maintain glucose homeostasis. In addition to glucose stimulation, insulin secretion is modulated by numerous G-protein coupled receptors (GPCRs). The GPCR ligands Kisspeptin-10 (KP) and glucagon-like peptide-1 (GLP-1) potentiate insulin secretion through Gq and Gs-coupled receptors, respectively. Despite many studies, the signaling mechanisms by which KP and GLP-1 potentiate insulin release are not thoroughly understood. We investigated the downstream signaling pathways of these ligands and their affects on cellular redox potential, intracellular calcium activity ([Ca2+]i), and insulin secretion from β-cells within intact murine islets. In contrast to previous studies performed on single β-cells, neither KP nor GLP-1 affect [Ca2+]i upon stimulation with glucose. KP significantly increases the cellular redox potential, while no effect is observed with GLP-1, suggesting that KP and GLP-1 potentiate insulin secretion through different mechanisms. Co-treatment with KP and the Gβγ-subunit inhibitor gallein inhibits insulin secretion similar to that observed with gallein alone, while co-treatment with gallein and GLP-1 does not differ from GLP-1 alone. In contrast, co-treatment with the Gβγ activator mSIRK and either KP or GLP-1 stimulates insulin release similar to mSIRK alone. Neither gallein nor mSIRK alter [Ca2+]i activity in the presence of KP or GLP-1. These data suggest that KP likely alters insulin secretion through a Gβγ-dependent process that stimulates glucose metabolism without altering Ca2+ activity, while GLP-1 does so, at least partly, through a Gα-dependent pathway that is independent of both metabolism and Ca2+. PMID:25401335

  16. Inhibition of voltage-gated potassium channels mediates uncarboxylated osteocalcin-regulated insulin secretion in rat pancreatic β cells.

    PubMed

    Gao, Jingying; Zhong, Xiangqin; Ding, Yaqin; Bai, Tao; Wang, Hui; Wu, Hongbin; Liu, Yunfeng; Yang, Jing; Zhang, Yi

    2016-04-15

    Insulin secretion from pancreatic β cells is important to maintain glucose homeostasis and is regulated by electrical activities. Uncarboxylated osteocalcin, a bone-derived protein, has been reported to regulate glucose metabolism by increasing insulin secretion, stimulating β cell proliferation and improving insulin sensitivity. But the underlying mechanisms of uncarboxylated osteocalcin-modulated insulin secretion remain unclear. In the present study, we investigated the relationship of uncarboxylated osteocalcin-regulated insulin secretion and voltage-gated potassium (KV) channels, voltage-gated calcium channels in rat β cells. Insulin secretion was measured by radioimmunoassay. Channel currents and membrane action potentials were recorded using the conventional whole-cell patch-clamp technique. Calcium imaging system was used to analyze intracellular Ca(2+) concentration ([Ca(2+)]i). The data show that under 16.7mmol/l glucose conditions uncarboxylated osteocalcin alone increased insulin secretion and [Ca(2+)]i, but with no such effects on insulin secretion and [Ca(2+)]i in the presence of a KV channel blocker, tetraethylammonium chloride. In the patch-clamp experiments, uncarboxylated osteocalcin lengthened action potential duration and significantly inhibited KV currents, but had no influence on the characteristics of voltage-gated calcium channels. These results indicate that KV channels are involved in uncarboxylated osteocalcin-regulated insulin secretion in rat pancreatic β cells. By inhibiting KV channels, uncarboxylated osteocalcin prolongs action potential duration, increases intracellular Ca(2+) concentration and finally promotes insulin secretion. This finding provides new insight into the mechanisms of osteocalcin-modulated insulin secretion.

  17. Intracellular and extracellular adenosine triphosphate in regulation of insulin secretion from pancreatic β cells (β).

    PubMed

    Wang, Chunjiong; Geng, Bin; Cui, Qinghua; Guan, Youfei; Yang, Jichun

    2014-03-01

    Adenosine triphosphate (ATP) synthesis and release in mitochondria play critical roles in regulating insulin secretion in pancreatic β cells. Mitochondrial dysfunction is mainly characterized by a decrease in ATP production, which is a central event in the progression of pancreatic β cell dysfunction and diabetes. ATP has been demonstrated to regulate insulin secretion via several pathways: (i) Intracellular ATP directly closes ATP-sensitive potassium channel to open L-type calcium channel, leading to an increase in free cytosolic calcium levels and exocytosis of insulin granules; (ii) A decrease in ATP production is always associated with an increase in production of reactive oxygen species, which exerts deleterious effects on pancreatic β cell survival and insulin secretion; and (iii) ATP can be co-secreted with insulin from pancreatic β cells, and the released ATP functions as an autocrine signal to modulate insulin secretory process via P2 receptors on the cell membrane. In this review, the recent findings regarding the role and mechanism of ATP synthesis and release in regulation of insulin secretion from pancreatic β cells will be summarized and discussed.

  18. Elevated Basal Insulin Secretion in Type 2 Diabetes Caused by Reduced Plasma Membrane Cholesterol

    PubMed Central

    Nagaraj, Vini; Kazim, Abdulla S.; Helgeson, Johan; Lewold, Clemens; Barik, Satadal; Buda, Pawel; Reinbothe, Thomas M.; Wennmalm, Stefan

    2016-01-01

    Elevated basal insulin secretion under fasting conditions together with insufficient stimulated insulin release is an important hallmark of type 2 diabetes, but the mechanisms controlling basal insulin secretion remain unclear. Membrane rafts exist in pancreatic islet cells and spatially organize membrane ion channels and proteins controlling exocytosis, which may contribute to the regulation of insulin secretion. Membrane rafts (cholesterol and sphingolipid containing microdomains) were dramatically reduced in human type 2 diabetic and diabetic Goto-Kakizaki (GK) rat islets when compared with healthy islets. Oxidation of membrane cholesterol markedly reduced microdomain staining intensity in healthy human islets, but was without effect in type 2 diabetic islets. Intriguingly, oxidation of cholesterol affected glucose-stimulated insulin secretion only modestly, whereas basal insulin release was elevated. This was accompanied by increased intracellular Ca2+ spike frequency and Ca2+ influx and explained by enhanced single Ca2+ channel activity. These results suggest that the reduced presence of membrane rafts could contribute to the elevated basal insulin secretion seen in type 2 diabetes. PMID:27533789

  19. Elevated Basal Insulin Secretion in Type 2 Diabetes Caused by Reduced Plasma Membrane Cholesterol.

    PubMed

    Nagaraj, Vini; Kazim, Abdulla S; Helgeson, Johan; Lewold, Clemens; Barik, Satadal; Buda, Pawel; Reinbothe, Thomas M; Wennmalm, Stefan; Zhang, Enming; Renström, Erik

    2016-10-01

    Elevated basal insulin secretion under fasting conditions together with insufficient stimulated insulin release is an important hallmark of type 2 diabetes, but the mechanisms controlling basal insulin secretion remain unclear. Membrane rafts exist in pancreatic islet cells and spatially organize membrane ion channels and proteins controlling exocytosis, which may contribute to the regulation of insulin secretion. Membrane rafts (cholesterol and sphingolipid containing microdomains) were dramatically reduced in human type 2 diabetic and diabetic Goto-Kakizaki (GK) rat islets when compared with healthy islets. Oxidation of membrane cholesterol markedly reduced microdomain staining intensity in healthy human islets, but was without effect in type 2 diabetic islets. Intriguingly, oxidation of cholesterol affected glucose-stimulated insulin secretion only modestly, whereas basal insulin release was elevated. This was accompanied by increased intracellular Ca(2+) spike frequency and Ca(2+) influx and explained by enhanced single Ca(2+) channel activity. These results suggest that the reduced presence of membrane rafts could contribute to the elevated basal insulin secretion seen in type 2 diabetes.

  20. Indices of insulin secretion during a liquid mixed-meal test in obese youth with diabetes

    USDA-ARS?s Scientific Manuscript database

    To compare indices of insulin secretion, insulin sensitivity (IS),and oral disposition index (oDI) during the liquid mixed-meal test in obese youth with clinically diagnosed type 2 diabetes mellitus (T2DM) and negative autoantibodies (Ab-) versus those with T2DM and positive autoantibodies (Ab+) to ...

  1. Intra- and Inter-Islet Synchronization of Metabolically Driven Insulin Secretion

    PubMed Central

    Pedersen, Morten Gram; Bertram, Richard; Sherman, Arthur

    2005-01-01

    Insulin secretion from pancreatic β-cells is pulsatile with a period of 5–10 min and is believed to be responsible for plasma insulin oscillations with similar frequency. To observe an overall oscillatory insulin profile it is necessary that the insulin secretion from individual β-cells is synchronized within islets, and that the population of islets is also synchronized. We have recently developed a model in which pulsatile insulin secretion is produced as a result of calcium-driven electrical oscillations in combination with oscillations in glycolysis. We use this model to investigate possible mechanisms for intra-islet and inter-islet synchronization. We show that electrical coupling is sufficient to synchronize both electrical bursting activity and metabolic oscillations. We also demonstrate that islets can synchronize by mutually entraining each other by their effects on a simple model “liver,” which responds to the level of insulin secretion by adjusting the blood glucose concentration in an appropriate way. Since all islets are exposed to the blood, the distributed islet-liver system can synchronize the individual islet insulin oscillations. Thus, we demonstrate how intra-islet and inter-islet synchronization of insulin oscillations may be achieved. PMID:15834002

  2. Ablation of TSC2 Enhances Insulin Secretion by Increasing the Number of Mitochondria through Activation of mTORC1

    PubMed Central

    Koyanagi, Maki; Asahara, Shun-ichiro; Matsuda, Tomokazu; Hashimoto, Naoko; Shigeyama, Yutaka; Shibutani, Yuki; Kanno, Ayumi; Fuchita, Megumi; Mikami, Tomoko; Hosooka, Tetsutya; Inoue, Hiroshi; Matsumoto, Michihiro; Koike, Masato; Uchiyama, Yasuo; Noda, Tetsuo; Seino, Susumu; Kasuga, Masato; Kido, Yoshiaki

    2011-01-01

    Aim We previously found that chronic tuberous sclerosis protein 2 (TSC2) deletion induces activation of mammalian target of rapamycin Complex 1 (mTORC1) and leads to hypertrophy of pancreatic beta cells from pancreatic beta cell-specific TSC2 knockout (βTSC2−/−) mice. The present study examines the effects of TSC2 ablation on insulin secretion from pancreatic beta cells. Methods Isolated islets from βTSC2−/− mice and TSC2 knockdown insulin 1 (INS-1) insulinoma cells treated with small interfering ribonucleic acid were used to investigate insulin secretion, ATP content and the expression of mitochondrial genes. Results Activation of mTORC1 increased mitochondrial DNA expression, mitochondrial density and ATP production in pancreatic beta cells of βTSC2−/− mice. In TSC2 knockdown INS-1 cells, mitochondrial DNA expression, mitochondrial density and ATP production were increased compared with those in control INS-1 cells, consistent with the phenotype of βTSC2−/− mice. TSC2 knockdown INS-1 cells also exhibited augmented insulin secretory response to glucose. Rapamycin inhibited mitochondrial DNA expression and ATP production as well as insulin secretion in response to glucose. Thus, βTSC2−/− mice exhibit hyperinsulinemia due to an increase in the number of mitochondria as well as enlargement of individual beta cells via activation of mTORC1. Conclusion Activation of mTORC1 by TSC2 ablation increases mitochondrial biogenesis and enhances insulin secretion from pancreatic beta cells. PMID:21886784

  3. Activation of Distinct P2Y Receptor Subtypes Stimulates Insulin Secretion in MIN6 Mouse Pancreatic β Cells

    PubMed Central

    Balasubramanian, Ramachandran; de Azua, Inigo Ruiz; Wess, Jürgen; Jacobson, Kenneth A.

    2010-01-01

    Extracellular nucleotides and their receptor antagonists have therapeutic potential in disorders such as inflammation, brain disorders, and cardiovascular diseases. Pancreatic β cells express several purinergic receptors, and reported nucleotide effects on insulin secretion are contradictory. We studied the effect of P2Y receptors on insulin secretion and cell death in MIN6, mouse pancreatic β cells. Expression of P2Y1 and P2Y6 receptors was revealed by total mRNA analysis using RT-PCR. MIN6 cells were stimulated in the presence of 16.7 mM glucose with or without P2Y1 and P2Y6 agonists, 2-MeSADP and Up3U, respectively. Both the agonists increased insulin secretion with EC50 values of 44.6±7.0 nM and 30.7±12.7 nM respectively. The insulin secretion by P2Y1 and P2Y6 agonists was blocked by their selective antagonists MRS2179 and MRS2578, respectively. Binding of the selective P2Y1 receptor antagonist radioligand [125I]MRS2500 in MIN6 cell membranes was saturable (KD 4.74±0.47 nM), and known P2Y1 ligands competed with high affinities. Inflammation and glucose toxicity leads to pancreatic β cell death in diabetes. Flow cytometric analysis revealed that Up3U but not 2-MeSADP protected MIN6 cells against TNF-α induced apoptosis. Overall, the results demonstrate that selective stimulation of P2Y1 and P2Y6 receptors increases insulin secretion that accompanies intracellular calcium release, suggesting potential application of P2Y receptor ligands in the treatment of diabetes. PMID:20067775

  4. Drp1 guarding of the mitochondrial network is important for glucose-stimulated insulin secretion in pancreatic beta cells

    SciTech Connect

    Reinhardt, Florian; Schultz, Julia; Waterstradt, Rica; Baltrusch, Simone

    2016-06-10

    Mitochondria form a tubular network in mammalian cells, and the mitochondrial life cycle is determined by fission, fusion and autophagy. Dynamin-related protein 1 (Drp1) has a pivotal role in these processes because it alone is able to constrict mitochondria. However, the regulation and function of Drp1 have been shown to vary between cell types. Mitochondrial morphology affects mitochondrial metabolism and function. In pancreatic beta cells mitochondrial metabolism is a key component of the glucose-induced cascade of insulin secretion. The goal of the present study was to investigate the action of Drp1 in pancreatic beta cells. For this purpose Drp1 was down-regulated by means of shDrp1 in insulin-secreting INS1 cells and mouse pancreatic islets. In INS1 cells reduced Drp1 expression resulted in diminished expression of proteins regulating mitochondrial fusion, namely mitofusin 1 and 2, and optic atrophy protein 1. Diminished mitochondrial dynamics can therefore be assumed. After down-regulation of Drp1 in INS1 cells and spread mouse islets the initially homogenous mitochondrial network characterised by a moderate level of interconnections shifted towards high heterogeneity with elongated, clustered and looped mitochondria. These morphological changes were found to correlate directly with functional alterations. Mitochondrial membrane potential and ATP generation were significantly reduced in INS1 cells after Drp1down-regulation. Finally, a significant loss of glucose-stimulated insulin secretion was demonstrated in INS1 cells and mouse pancreatic islets. In conclusion, Drp1 expression is important in pancreatic beta cells to maintain the regulation of insulin secretion. -- Highlights: •Down-regulation of Drp1 in INS1 cells reduces mitochondrial fusion protein expression. •Mitochondrial membrane potential in INS1 cells is diminished after Drp1 down-regulation. •Mitochondria become elongated after down-regulation of Drp1 in beta cells. •Down-regulation of

  5. Novel Small Molecule Glucagon-Like Peptide-1 Receptor Agonist Stimulates Insulin Secretion in Rodents and From Human Islets

    PubMed Central

    Sloop, Kyle W.; Willard, Francis S.; Brenner, Martin B.; Ficorilli, James; Valasek, Kathleen; Showalter, Aaron D.; Farb, Thomas B.; Cao, Julia X.C.; Cox, Amy L.; Michael, M. Dodson; Gutierrez Sanfeliciano, Sonia Maria; Tebbe, Mark J.; Coghlan, Michael J.

    2010-01-01

    OBJECTIVE The clinical effectiveness of parenterally-administered glucagon-like peptide-1 (GLP-1) mimetics to improve glucose control in patients suffering from type 2 diabetes strongly supports discovery pursuits aimed at identifying and developing orally active, small molecule GLP-1 receptor agonists. The purpose of these studies was to identify and characterize novel nonpeptide agonists of the GLP-1 receptor. RESEARCH DESIGN AND METHODS Screening using cells expressing the GLP-1 receptor and insulin secretion assays with rodent and human islets were used to identify novel molecules. The intravenous glucose tolerance test (IVGTT) and hyperglycemic clamp characterized the insulinotropic effects of compounds in vivo. RESULTS Novel low molecular weight pyrimidine-based compounds that activate the GLP-1 receptor and stimulate glucose-dependent insulin secretion are described. These molecules induce GLP-1 receptor-mediated cAMP signaling in HEK293 cells expressing the GLP-1 receptor and increase insulin secretion from rodent islets in a dose-dependent manner. The compounds activate GLP-1 receptor signaling, both alone or in an additive fashion when combined with the endogenous GLP-1 peptide; however, these agonists do not compete with radiolabeled GLP-1 in receptor-binding assays. In vivo studies using the IVGTT and the hyperglycemic clamp in Sprague Dawley rats demonstrate increased insulin secretion in compound-treated animals. Further, perifusion assays with human islets isolated from a donor with type 2 diabetes show near-normalization of insulin secretion upon compound treatment. CONCLUSIONS These studies characterize the insulinotropic effects of an early-stage, small molecule GLP-1 receptor agonist and provide compelling evidence to support pharmaceutical optimization. PMID:20823098

  6. Stress-impaired transcription factor expression and insulin secretion in transplanted human islets

    PubMed Central

    Dai, Chunhua; Kayton, Nora S.; Shostak, Alena; Poffenberger, Greg; Cyphert, Holly A.; Aramandla, Radhika; Thompson, Courtney; Papagiannis, Ioannis G.; Shiota, Masakazu; Stafford, John M.; Greiner, Dale L.; Herrera, Pedro L.; Shultz, Leonard D.; Stein, Roland; Powers, Alvin C.

    2016-01-01

    Type 2 diabetes is characterized by insulin resistance, hyperglycemia, and progressive β cell dysfunction. Excess glucose and lipid impair β cell function in islet cell lines, cultured rodent and human islets, and in vivo rodent models. Here, we examined the mechanistic consequences of glucotoxic and lipotoxic conditions on human islets in vivo and developed and/or used 3 complementary models that allowed comparison of the effects of hyperglycemic and/or insulin-resistant metabolic stress conditions on human and mouse islets, which responded quite differently to these challenges. Hyperglycemia and/or insulin resistance impaired insulin secretion only from human islets in vivo. In human grafts, chronic insulin resistance decreased antioxidant enzyme expression and increased superoxide and amyloid formation. In human islet grafts, expression of transcription factors NKX6.1 and MAFB was decreased by chronic insulin resistance, but only MAFB decreased under chronic hyperglycemia. Knockdown of NKX6.1 or MAFB expression in a human β cell line recapitulated the insulin secretion defect seen in vivo. Contrary to rodent islet studies, neither insulin resistance nor hyperglycemia led to human β cell proliferation or apoptosis. These results demonstrate profound differences in how excess glucose or lipid influence mouse and human insulin secretion and β cell activity and show that reduced expression of key islet-enriched transcription factors is an important mediator of glucotoxicity and lipotoxicity. PMID:27064285

  7. Aldosterone decreases glucose-stimulated insulin secretion in vivo in mice and in murine islets

    PubMed Central

    Luo, P.; Kreger, M. T.; Brissova, M.; Dai, C.; Whitfield, T. T.; Kim, H. S.; Wasserman, D. H.; Powers, A. C.; Brown, N. J.

    2011-01-01

    Aims/hypothesis Aldosterone concentrations increase in obesity and predict the onset of diabetes. We investigated the effects of aldosterone on glucose homeostasis and insulin secretion in vivo and in vitro. Methods We assessed insulin sensitivity and insulin secretion in aldosterone synthase-deficient (As [also known as Cyp11b2]−/−)and wild-type mice using euglycaemic-hyperinsulinaemic and hyperglycaemic clamps, respectively. We also conducted studies during high sodium intake to normalise renin activity and potassium concentration in As−/− mice. We subsequently assessed the effect of aldosterone on insulin secretion in vitro in the presence or absence of mineralocorticoid receptor antagonists in isolated C57BL/6J islets and in the MIN6 beta cell line. Results Fasting glucose concentrations were reduced in As−/−mice compared with wild-type. During hyperglycaemic clamps, insulin and C-peptide concentrations increased to a greater extent in As−/− than in wild-type mice. This was not attributable to differences in potassium or angiotensin II, as glucose-stimulated insulin secretion was enhanced in As−/− mice even during high sodium intake. There was no difference in insulin sensitivity between As−/− and wild-type mice in euglycaemic-hyperinsulinaemic clamp studies. In islet and MIN6 beta cell studies, aldosterone inhibited glucose and isobutylmethylxanthine-stimulated insulin secretion, an effect that was not blocked by mineralocorticoid receptor antagonism, but was prevented by the superoxide dismutase mimetic tempol. Conclusions/interpretation We demonstrated that aldosterone deficiency or excess modulates insulin secretion in vivo and in vitro via reactive oxygen species and in a manner that is independent of mineralocorticoid receptors. These findings provide insight into the mechanism of glucose intolerance in conditions of relative aldosterone excess. PMID:21519965

  8. Chronic leucine exposure results in reduced but reversible glucose-stimulated insulin secretion in INS-1 cells.

    PubMed

    Zhang, Xiujuan; Han, Wenxia; Jiang, Xiuyun; Li, Min; Gao, Ling; Zhao, Jia Jun

    2014-06-01

    Previous studies have demonstrated that sustained high leucine exposure decreases glucose-stimulated insulin secretion (GSIS). However, whether this effect is recoverable following the removal of leucine is unclear. Pancreatic/duodenal homeobox-1 (PDX-1) and its downstream target, glucose transporter 2 (GLUT2), are reported to be positively associated with insulin secretion. However, it also remains unclear whether the effect of leucine on GSIS is accompanied by alterations in PDX-1 and GLUT2. In the present study, insulin secretion, insulin content, PDX-1 and GLUT2 protein expression in INS-1 (rat insulinoma cell line) cells were assessed following a 24-h incubation in 40 mmol/l leucine. Half of the cells were incubated in leucine-free media for a further 24 h to observe the abovementioned effects. In contrast to the control, 40 mmol/l leucine for 24 or 48 h diminished GSIS at high glucose concentrations by 11% (P=0.026) or 22% (P=0.003), insulin content by 14% (P=0.008) or 20% (P=0.002), as well as decreasing PDX-1 and GLUT2 expression. When leucine was removed from the media for a further 24-h incubation, in comparison with those cells that were maintained in leucine treatment for 24 and 48 h, the high GSIS increased by 13% (P=0.032) and 27% (P=0.002), insulin content was augmented by 10% (P=0.014) and 20% (P=0.003), and the protein expression of PDX-1 and GLUT2 also increased. The present study demonstrates that sustained high concentrations of leucine induce a reversible impairment of GSIS and alter insulin content, which is mediated by PDX-1 and GLUT2, in INS-1 cells.

  9. Inhibitory effect of kisspeptins on insulin secretion from isolated mouse islets.

    PubMed

    Vikman, J; Ahrén, B

    2009-11-01

    Islet hormone secretion is regulated by a variety of factors, and many of these signal through G protein-coupled receptors (GPCRs). A novel islet GPCR is GPR54, which couples to the Gq isoform of G proteins, which in turn signal through the phospholipase C pathway. Ligands for GPR54 are kisspeptins, which are peptides encoded in the KISS1 gene and also expressed in islet beta-cells. The KISS1 gene encodes a hydrophobic 145-amino acid protein that is cleaved into a 54-amino acid protein, kisspeptin-54 or KP54. Shorter kisspeptins also exist, such as kisspeptin-10 (KP10) and kisspeptin-13 (KP13). The involvement of GPR54 and kisspeptins in the regulation of islet function is not known. To address this problem, we incubated isolated mouse islets in the presence of KP13 and KP54 for 60 min and measured insulin secretion. We found that both KP13 and KP54 at 10 nM, 100 nM and 1microM inhibited insulin secretion in the presence of 2.8 mM glucose. However, by increasing the glucose concentration, this inhibitory action of the kisspeptins vanished. Thus, at 11.1 mM glucose, KP13 and KP54 inhibited insulin secretion only at high doses, and at 16.7 mM they no longer inhibited insulin secretion in any of the doses. We conclude that kisspeptins inhibit insulin secretion at glucose concentrations below 11.1 mM. This suggests that kisspeptins are regulating insulin secretion at physiological concentrations of glucose. The mechanisms by which kisspeptins regulate islet function and insulin secretion are unknown and will be further investigated.

  10. Effects of intracerebroventricular (ICV) olanzapine on insulin sensitivity and secretion in vivo: an animal model.

    PubMed

    Hahn, Margaret K; Chintoh, Araba; Remington, Gary; Teo, Celine; Mann, Steve; Arenovich, Tamara; Fletcher, Paul; Lam, Loretta; Nobrega, Jose; Guenette, Melanie; Cohn, Tony; Giacca, Adria

    2014-03-01

    The atypical antipsychotics (AAPs) have been associated with an increased risk of type 2 diabetes. While weight gain associated with AAPs is a risk factor for diabetes, preclinical work suggests that among these medications, olanzapine, when given peripherally in a single dose, causes pronounced effects on insulin sensitivity and secretion. Given a critical role of the hypothalamus in control of glucose metabolism, we examined the effect of central administration of olanzapine. Sprague-Dawley rats were treated with a single 75 μg intracerebroventricular (ICV) dose of olanzapine and tested using separate hyperinsulinemic-euglycemic and hyperglycemic clamps. Dosing of olanzapine was established based on inhibition of amphetamine-induced locomotion. In contrast to the single dosing peripheral paradigm, there was no effect of central olanzapine on insulin sensitivity, either with respect to hepatic glucose production or peripheral glucose uptake. Analogous to the peripheral model, a single ICV dose of olanzapine followed by the hyperglycemic clamp decreased insulin (p=0.0041) and C-peptide response (p=0.0039) to glucose challenge as compared to vehicle, mirrored also by a decrease in the steady state glucose infusion rate required to maintain hyperglycemia (p=0.002). In conclusion, we demonstrate novel findings that at least part of the effect of olanzapine on beta-cell function in vivo is central.

  11. Norepinephrine inhibits islet lipid metabolism, sup 45 Ca sup 2+ uptake, and insulin secretion

    SciTech Connect

    Vara, E.; Tamarit-Rodriguez, J. )

    1989-12-01

    We have previously shown that palmitate potentiates, in isolated islets, glucose-induced stimulation of insulin release, de novo lipid synthesis, and {sup 45}Ca{sup 2+} turnover in a correlative manner. Norepinephrine, a known inhibitor of the secretory response, has now been used to further investigate the relationships among the three phenomena. The amine decreased insulin secretion dose dependently in response to glucose and palmitate with alpha 2-adrenergic specificity. It also reduced similarly the oxidation of 1 mmol/l (U-{sup 14}C)palmitate as well as the incorporation of 20 mmol/l D-(U-{sup 14}C)glucose into islet phospholipids and neutral lipids through an alpha 2-adrenergic mechanism. These results indirectly suggest that alpha 2-adrenoceptor stimulation inhibits in islets both palmitate oxidation and esterification through an inactivation of long-chain acyl-CoA synthetase and other enzymes of glycerolipid synthesis. Islet uptake of {sup 45}Ca{sup 2+} was also decreased by norepinephrine with a similar sensitivity to that shown by insulin release and de novo lipid synthesis. Therefore, it is suggested that alpha 2-adrenoceptor-mediated reduction of the potentiation by palmitate of the secretory response to glucose depends on the inhibition of fatty acid metabolism and the resulting impairment of de novo lipid synthesis and {sup 45}Ca{sup 2+} turnover.

  12. Effects of Steaming Time and Frequency for Manufactured Red Liriope platyphylla on the Insulin Secretion Ability and Insulin Receptor Signaling Pathway

    PubMed Central

    Choi, Sun Il; Lee, Hye Ryun; Goo, Jun Seo; Kim, Ji Eun; Nam, So Hee; Hwang, In Sik; Lee, Young Ju; Prak, So Hae; Lee, Hee Seob; Lee, Jong Sup; Jang, In Surk; Son, Hong Ju

    2011-01-01

    In oriental medicine, Liriope platyphylla (LP) has long been regarded as a curative herb useful for the treatment of diabetes, asthma, and neurodegenerative disorders. The principal objective of this study was to assess the effects of steaming time and frequency for manufactured Red LP (RLP) on insulin secretion ability and insulin receptor signaling pathway. To achieve our goal, several types of LPs manufactured under different conditions were applied to INS cells and streptozotocin (STZ)-induced diabetic ICR mice, after which alterations in insulin concentrations were detected in the culture supernatants and sera. The optimal concentration for the investigation of insulin secretion ability was found to be 50 ug/mL of LP. At this concentration, maximum insulin secretion was observed in the INS cells treated with LP extract steamed for 3 h (3-SLP) with two repeated steps (3 h steaming and 24 h air-dried) carried out 9 times (9-SALP); no significant changes in viability were detected in any of the treated cells. Additionally, the expression and phosphorylation levels of most components in the insulin receptor signaling pathway were increased significantly in the majority of cells treated with steaming-processed LP as compared to the cells treated with LP prepared without steaming. With regard to glucose transporter (GLUT) expression, alterations of steaming time induced similar responses on the expression levels of GLUT-2 and GLUT-3. However, differences in steaming frequency were also shown to induce dose-dependent responses in the expression level of GLUT-2 only; no significant differences in GLUT-3 expression were detected under these conditions. Furthermore, these responses observed in vitro were similarly detected in STZ-induced diabetic mice. 24-SLP and 9-SALP treatment applied for 14 days induced the down-regulation of glucose concentration and upregulation of insulin concentration. Therefore, these results indicated that the steaming processed LP may

  13. Measuring phospholipase D activity in insulin-secreting pancreatic beta-cells and insulin-responsive muscle cells and adipocytes.

    PubMed

    Cazzolli, Rosanna; Huang, Ping; Teng, Shuzhi; Hughes, William E

    2009-01-01

    Phospholipase D (PLD) is an enzyme producing phosphatidic acid and choline through hydrolysis of phosphatidylcholine. The enzyme has been identified as a member of a variety of signal transduction cascades and as a key regulator of numerous intracellular vesicle trafficking processes. A role for PLD in regulating glucose homeostasis is emerging as the enzyme has recently been identified in events regulating exocytosis of insulin from pancreatic beta-cells and also in insulin-stimulated glucose uptake through controlling GLUT4 vesicle exocytosis in muscle and adipose tissue. We present methodologies for assessing cellular PLD activity in secretagogue-stimulated insulin-secreting pancreatic beta-cells and also insulin-stimulated adipocyte and muscle cells, two of the principal insulin-responsive cell types controlling blood glucose levels.

  14. Lysosomal integral membrane protein Sidt2 plays a vital role in insulin secretion.

    PubMed

    Gao, Jialin; Yu, Cui; Xiong, Qianyin; Zhang, Yao; Wang, Lizhuo

    2015-01-01

    Abnormal insulin secretion results in impaired glucose tolerance and is one of the causal factors in the etiology of type 2 diabetes mellitus. Sidt2, a lysosomal integral membrane protein, plays a critical role in insulin secretion. Here, we further investigate its regulation in insulin secretion. We show that Sidt2(-/-) mice exhibit weight loss, decreased postnatal survival rate with aging, increased fasting glucose and impaired glucose tolerance. After loading high levels of glucose in their diet, Sidt2(-/-) mice produce notably lower insulin levels at the first-phase secretion compared with Sidt2(+/+) mice. Consistent with the in vivo study, INS-1 cells treated with Sidt2 siRNA produced less insulin when loaded with 16.7 mM of glucose. Only 2 of the 13 genes, synap1 and synap3 which encode soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins, showed significantly decreased expression in Sidt2(-/-) mice. In conclusion, Sdit2 may play a vital role in the regulation of insulin secretion via two SNARE proteins synap1 and syanp3.

  15. Acute Glucagon Induces Postprandial Peripheral Insulin Resistance

    PubMed Central

    Patarrão, Rita S.; Lautt, W. Wayne; Macedo, M. Paula

    2015-01-01

    Glucagon levels are often moderately elevated in diabetes. It is known that glucagon leads to a decrease in hepatic glutathione (GSH) synthesis that in turn is associated with decreased postprandial insulin sensitivity. Given that cAMP pathway controls GSH levels we tested whether insulin sensitivity decreases after intraportal (ipv) administration of a cAMP analog (DBcAMP), and investigated whether glucagon promotes insulin resistance through decreasing hepatic GSH levels.Insulin sensitivity was determined in fed male Sprague-Dawley rats using a modified euglycemic hyperinsulinemic clamp in the postprandial state upon ipv administration of DBcAMP as well as glucagon infusion. Glucagon effects on insulin sensitivity was assessed in the presence or absence of postprandial insulin sensitivity inhibition by administration of L-NMMA. Hepatic GSH and NO content and plasma levels of NO were measured after acute ipv glucagon infusion. Insulin sensitivity was assessed in the fed state and after ipv glucagon infusion in the presence of GSH-E. We founf that DBcAMP and glucagon produce a decrease of insulin sensitivity, in a dose-dependent manner. Glucagon-induced decrease of postprandial insulin sensitivity correlated with decreased hepatic GSH content and was restored by administration of GSH-E. Furthermore, inhibition of postprandial decrease of insulin sensitivity L-NMMA was not overcome by glucagon, but glucagon did not affect hepatic and plasma levels of NO. These results show that glucagon decreases postprandial insulin sensitivity through reducing hepatic GSH levels, an effect that is mimicked by increasing cAMP hepatic levels and requires physiological NO levels. These observations support the hypothesis that glucagon acts via adenylate cyclase to decrease hepatic GSH levels and induce insulin resistance. We suggest that the glucagon-cAMP-GSH axis is a potential therapeutic target to address insulin resistance in pathological conditions. PMID:25961284

  16. Acute glucagon induces postprandial peripheral insulin resistance.

    PubMed

    Patarrão, Rita S; Lautt, W Wayne; Macedo, M Paula

    2015-01-01

    Glucagon levels are often moderately elevated in diabetes. It is known that glucagon leads to a decrease in hepatic glutathione (GSH) synthesis that in turn is associated with decreased postprandial insulin sensitivity. Given that cAMP pathway controls GSH levels we tested whether insulin sensitivity decreases after intraportal (ipv) administration of a cAMP analog (DBcAMP), and investigated whether glucagon promotes insulin resistance through decreasing hepatic GSH levels.Insulin sensitivity was determined in fed male Sprague-Dawley rats using a modified euglycemic hyperinsulinemic clamp in the postprandial state upon ipv administration of DBcAMP as well as glucagon infusion. Glucagon effects on insulin sensitivity was assessed in the presence or absence of postprandial insulin sensitivity inhibition by administration of L-NMMA. Hepatic GSH and NO content and plasma levels of NO were measured after acute ipv glucagon infusion. Insulin sensitivity was assessed in the fed state and after ipv glucagon infusion in the presence of GSH-E. We founf that DBcAMP and glucagon produce a decrease of insulin sensitivity, in a dose-dependent manner. Glucagon-induced decrease of postprandial insulin sensitivity correlated with decreased hepatic GSH content and was restored by administration of GSH-E. Furthermore, inhibition of postprandial decrease of insulin sensitivity L-NMMA was not overcome by glucagon, but glucagon did not affect hepatic and plasma levels of NO. These results show that glucagon decreases postprandial insulin sensitivity through reducing hepatic GSH levels, an effect that is mimicked by increasing cAMP hepatic levels and requires physiological NO levels. These observations support the hypothesis that glucagon acts via adenylate cyclase to decrease hepatic GSH levels and induce insulin resistance. We suggest that the glucagon-cAMP-GSH axis is a potential therapeutic target to address insulin resistance in pathological conditions.

  17. The Relationship between 25-hydroxyvitamin D Levels, Insulin Sensitivity and Insulin Secretion in Women 3 Years after Delivery.

    PubMed

    Tänczer, Tímea; Magenheim, Rita; Fürst, Ágnes; Domján, Beatrix; Janicsek, Zsófia; Szabó, Eszter; Ferencz, Viktória; Tabák, Ádám G

    2017-05-03

    There is a direct correlation between 25-hydroxyvitamin D (25[OH]D) levels and insulin sensitivity. Furthermore, women with gestational diabetes (GDM) may have lower levels of 25(OH)D compared to controls. The present study intended to investigate 25(OH)D levels and their association with insulin sensitivity and insulin secretion in women with prior GDM and in controls 3.2 years after delivery. A total of 87 patients with prior GDM and 45 randomly selected controls (age range, 22 to 44 years) with normal glucose tolerance during pregnancy nested within a cohort of all deliveries at Saint Margit Hospital, Budapest, between January 1 2005, and December 31 2006, were examined. Their 25(OH) D levels were measured by radioimmunoassay. Insulin sensitivity and fasting insulin secretion were estimated using the homeostasis model asssessment (HOMA) calculator and early insulin secretion by the insulinogenic index based on a 75 g oral glucose tolerance test. There was no significant difference in 25(OH)D levels between cases and controls (27.2±13.1 [±SD] vs. 26.9±9.8 ng/L). There was a positive association between HOMA insulin sensitivity and 25(OH)D levels (beta = 0.017; 95% CI 0.001 to 0.034/1 ng/mL) that was robust to adjustment for age and body mass index. There was a nonsignificant association between HOMA insulin secretion and 25(OH)D (p=0.099), while no association was found with the insulinogenic index. Prior GDM status was not associated with 25(OH)D levels; however, 25(OH) D levels were associated with HOMA insulin sensitivity. It is hypothesized that the association between HOMA insulin secretion and 25(OH)D levels is related to the autoregulation of fasting glucose levels because no association between 25(OH)D and insulinogenic index was found. Copyright © 2017 Canadian Diabetes Association. Published by Elsevier Inc. All rights reserved.

  18. Misunderstandings and controversies about the insulin-secreting properties of antidiabetic sulfonylureas.

    PubMed

    Henquin, Jean-Claude

    2017-07-12

    After 60 years of use in the treatment of type 2 diabetes, hypoglycemic sulfonylureas remain a recommended option in current therapeutic charts. Their binding to sulfonylurea receptor-1, the regulatory subunit of ATP-sensitive potassium channels in the plasma membrane of pancreatic β-cells, leads to closure of the channels, membrane depolarization and influx of Ca(2+) through voltage-gated calcium channels. The resulting increase in cytosolic Ca(2+) triggers exocytosis of insulin granules. Sulfonylureas and glucose thus produce the same triggering signal but, unlike sulfonylureas, glucose does so via acceleration of β-cell metabolism. Glucose metabolism also produces amplifying signals that approximately double the secretory response to triggering Ca(2+). One persistent misunderstanding about sulfonylureas is the alleged glucose-independence of their effects. It is correct that high concentrations of these drugs can induce insulin secretion in low glucose and cause hypoglycemic episodes in treated patients. Conversely, that untoward effect is erroneously considered as evidence that their therapeutic action is independent of glucose. Another evolving controversy about the action of sulfonylureas in β-cells is whether, like glucose, they also produce intracellular amplifying signals able to augment the efficacy of Ca(2+) on exocytosis. The aims of this review are to dissipate the misunderstanding and discuss the controversy. Reasons why proposed amplifying effects of sulfonylureas are unlikely to be relevant for their action in vivo will be presented. Possible interactions of sulfonylureas and glucagon-like peptide-1 in β-cells will be discussed. Mechanisms whereby the ambient glucose concentration modulates the insulin-secreting action of therapeutic concentrations of sulfonylureas will be explained. Copyright © 2017 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM). All rights reserved.

  19. Defective insulin secretion in pancreatic β cells lacking type 1 IGF receptor

    PubMed Central

    Xuan, Shouhong; Kitamura, Tadahiro; Nakae, Jun; Politi, Katerina; Kido, Yoshiaki; Fisher, Peter E.; Morroni, Manrico; Cinti, Saverio; White, Morris F.; Herrera, Pedro L.; Accili, Domenico; Efstratiadis, Argiris

    2002-01-01

    Defective insulin secretion is a feature of type 2 diabetes that results from inadequate compensatory increase of β cell mass and impaired glucose-dependent insulin release. β cell proliferation and secretion are thought to be regulated by signaling through receptor tyrosine kinases. In this regard, we sought to examine the potential proliferative and/or antiapoptotic role of IGFs in β cells by tissue-specific conditional mutagenesis ablating type 1 IGF receptor (IGF1R) signaling. Unexpectedly, lack of functional IGF1R did not affect β cell mass, but resulted in age-dependent impairment of glucose tolerance, associated with a decrease of glucose- and arginine-dependent insulin release. These observations reveal a requirement of IGF1R-mediated signaling for insulin secretion. PMID:12370279

  20. Mechanisms of amino acid-stimulated insulin secretion in congenital hyperinsulinism.

    PubMed

    Zhang, Tingting; Li, Changhong

    2013-01-01

    The role of amino acids in the regulation of insulin secretion in pancreatic beta-cells is highlighted in three forms of congenital hyperinsulinism (HI), namely gain-of-function mutations of glutamate dehydrogenase (GDH), loss-of-function mutations of ATP-dependent potassium channels, and a deficiency of short-chain 3-hydroxyacyl-CoA dehydrogenase. Studies on disease mouse models of HI suggest that amino acid oxidation and signaling effects are the major mechanisms of amino acid-stimulated insulin secretion. Amino acid oxidation via GDH produces ATP and triggers insulin secretion. The signaling effect of amino acids amplifies insulin release after beta-cell depolarization and elevation of cytosolic calcium.

  1. Mechanisms of enhanced insulin secretion and sensitivity with n-3 unsaturated fatty acids.

    PubMed

    Bhaswant, Maharshi; Poudyal, Hemant; Brown, Lindsay

    2015-06-01

    The widespread acceptance that increased dietary n-3 polyunsaturated fatty acids (PUFAs), especially α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), improve health is based on extensive studies in animals, isolated cells and humans. Visceral adiposity is part of the metabolic syndrome, together with insulin resistance, dyslipidemia, hypertension and inflammation. Alleviation of metabolic syndrome requires normalization of insulin release and responses. This review assesses our current knowledge of the mechanisms that allow n-3 PUFAs to improve insulin secretion and sensitivity. EPA has been more extensively studied than either ALA or DHA. The complex actions of EPA include increased G-protein-receptor-mediated release of glucagon-like peptide 1 (GLP-1) from enteroendocrine L-cells in the intestine, up-regulation of the apelin pathway and down-regulation of other control pathways to promote insulin secretion by the pancreatic β-cells, together with suppression of inflammatory responses to adipokines, inhibition of peroxisome proliferator-activated receptor α actions and prevention of decreased insulin-like growth factor-1 secretion to improve peripheral insulin responses. The receptors involved and the mechanisms of action probably differ for ALA and DHA, with antiobesity effects predominating for ALA and anti-inflammatory effects for DHA. Modifying both GLP-1 release and the actions of adipokines by n-3 PUFAs could lead to additive improvements in both insulin secretion and sensitivity.

  2. Functional Reconstitution of the Insulin-Secreting Porosome Complex in Live Cells.

    PubMed

    Naik, Akshata R; Kulkarni, Sanjana P; Lewis, Kenneth T; Taatjes, Douglas J; Jena, Bhanu P

    2016-01-01

    Supramolecular cup-shaped lipoprotein structures called porosomes embedded in the cell plasma membrane mediate fractional release of intravesicular contents from cells during secretion. The presence of porosomes, have been documented in many cell types including neurons, acinar cells of the exocrine pancreas, GH-secreting cells of the pituitary, and insulin-secreting pancreatic β-cells. Functional reconstitution of porosomes into artificial lipid membranes, have also been accomplished. Earlier studies on mouse insulin-secreting Min6 cells report 100-nm porosome complexes composed of nearly 30 proteins. In the current study, porosomes have been functionally reconstituted for the first time in live cells. Isolated Min6 porosomes reconstituted into live Min6 cells demonstrate augmented levels of porosome proteins and a consequent increase in the potency and efficacy of glucose-stimulated insulin release. Elevated glucose-stimulated insulin secretion 48 hours after reconstitution, reflects on the remarkable stability and viability of reconstituted porosomes, documenting the functional reconstitution of native porosomes in live cells. These results, establish a new paradigm in porosome-mediated insulin secretion in β-cells.

  3. Early enhancements of hepatic and later of peripheral insulin sensitivity combined with increased postprandial insulin secretion contribute to improved glycemic control after Roux-en-Y gastric bypass.

    PubMed

    Bojsen-Møller, Kirstine N; Dirksen, Carsten; Jørgensen, Nils B; Jacobsen, Siv H; Serup, Annette K; Albers, Peter H; Hansen, Dorte L; Worm, Dorte; Naver, Lars; Kristiansen, Viggo B; Wojtaszewski, Jørgen F P; Kiens, Bente; Holst, Jens J; Richter, Erik A; Madsbad, Sten

    2014-05-01

    Roux-en-Y gastric bypass (RYGB) improves glycemic control within days after surgery, and changes in insulin sensitivity and β-cell function are likely to be involved. We studied 10 obese patients with type 2 diabetes (T2D) and 10 obese glucose-tolerant subjects before and 1 week, 3 months, and 1 year after RYGB. Participants were included after a preoperative diet-induced total weight loss of -9.2 ± 1.2%. Hepatic and peripheral insulin sensitivity were assessed using the hyperinsulinemic- euglycemic clamp combined with the glucose tracer technique, and β-cell function was evaluated in response to an intravenous glucose-glucagon challenge as well as an oral glucose load. Within 1 week, RYGB reduced basal glucose production, improved basal hepatic insulin sensitivity, and increased insulin clearance, highlighting the liver as an important organ responsible for early effects on glucose metabolism after surgery. Insulin-mediated glucose disposal and suppression of fatty acids did not improve immediately after surgery but increased at 3 months and 1 year; this increase likely was related to the reduction in body weight. Insulin secretion increased after RYGB only in patients with T2D and only in response to oral glucose, underscoring the importance of the changed gut anatomy.

  4. CNC-bZIP protein Nrf1-dependent regulation of glucose-stimulated insulin secretion.

    PubMed

    Zheng, Hongzhi; Fu, Jingqi; Xue, Peng; Zhao, Rui; Dong, Jian; Liu, Dianxin; Yamamoto, Masayuki; Tong, Qingchun; Teng, Weiping; Qu, Weidong; Zhang, Qiang; Andersen, Melvin E; Pi, Jingbo

    2015-04-01

    The inability of pancreatic β-cells to secrete sufficient insulin in response to glucose stimulation is a major contributing factor to the development of type 2 diabetes (T2D). We investigated both the in vitro and in vivo effects of deficiency of nuclear factor-erythroid 2-related factor 1 (Nrf1) in β-cells on β-cell function and glucose homeostasis. Silencing of Nrf1 in β-cells leads to a pre-T2D phenotype with disrupted glucose metabolism and impaired insulin secretion. Specifically, MIN6 β-cells with stable knockdown of Nrf1 (Nrf1-KD) and isolated islets from β-cell-specific Nrf1-knockout [Nrf1(b)-KO] mice displayed impaired glucose responsiveness, including elevated basal insulin release and decreased glucose-stimulated insulin secretion (GSIS). Nrf1(b)-KO mice exhibited severe fasting hyperinsulinemia, reduced GSIS, and glucose intolerance. Silencing of Nrf1 in MIN6 cells resulted in oxidative stress and altered glucose metabolism, with increases in both glucose uptake and aerobic glycolysis, which is associated with the elevated basal insulin release and reduced glucose responsiveness. The elevated glycolysis and reduced glucose responsiveness due to Nrf1 silencing likely result from altered expression of glucose metabolic enzymes, with induction of high-affinity hexokinase 1 and suppression of low-affinity glucokinase. Our study demonstrated a novel role of Nrf1 in regulating glucose metabolism and insulin secretion in β-cells and characterized Nrf1 as a key transcription factor that regulates the coupling of glycolysis and mitochondrial metabolism and GSIS. Nrf1 plays critical roles in regulating glucose metabolism, mitochondrial function, and insulin secretion, suggesting that Nrf1 may be a novel target to improve the function of insulin-secreting β-cells.

  5. Reactive Oxygen Species Stimulate Insulin Secretion in Rat Pancreatic Islets: Studies Using Mono-Oleoyl-Glycerol

    PubMed Central

    Kane, Ada; Shirihai, Orian; Corkey, Barbara E.; Deeney, Jude T.

    2012-01-01

    Chronic exposure (24–72 hrs) of pancreatic islets to elevated glucose and fatty acid leads to glucolipoxicity characterized by basal insulin hypersecretion and impaired glucose-stimulated insulin secretion (GSIS). Our aim was to determine the mechanism for basal hypersecretion of insulin. We used mono-oleoyl-glycerol (MOG) as a tool to rapidly increase lipids in isolated rat pancreatic ß-cells and in the clonal pancreatic ß-cell line INS-1 832/13. MOG (25–400 µM) stimulated basal insulin secretion from ß-cells in a concentration dependent manner without increasing intracellular Ca2+ or O2 consumption. Like GSIS, MOG increased NAD(P)H and reactive oxygen species (ROS). The mitochondrial reductant ß-hydroxybutyrate (ß-OHB) also increased the redox state and ROS production, while ROS scavengers abrogated secretion. Diazoxide (0.4 mM) did not prevent the stimulatory effect of MOG, confirming that the effect was independent of the KATP-dependent pathway of secretion. MOG was metabolized to glycerol and long-chain acyl-CoA (LC-CoA), whereas, acute oleate did not similarly increase LC-CoA. Inhibition of diacylglycerol kinase (DGK) did not mimic the effect of MOG on insulin secretion, indicating that MOG did not act primarily by inhibiting DGK. Inhibition of acyl-CoA synthetase (ACS) reduced the stimulatory effect of MOG on basal insulin secretion by 30% indicating a role for LC-CoA. These data suggest that basal insulin secretion is stimulated by increased ROS production, due to an increase in the mitochondrial redox state independent of the established components of GSIS. PMID:22272304

  6. Sodium arsenite impairs insulin secretion and transcription in pancreatic {beta}-cells

    SciTech Connect

    Diaz-Villasenor, Andrea; Sanchez-Soto, M. Carmen; Cebrian, Mariano E.; Ostrosky-Wegman, Patricia; Hiriart, Marcia . E-mail: mhiriart@ifc.unam.mx

    2006-07-01

    Human studies have shown that chronic inorganic arsenic (iAs) exposure is associated with a high prevalence and incidence of type 2 diabetes. However, the mechanism(s) underlying this effect are not well understood, and practically, there is no information available on the effects of arsenic on pancreatic {beta}-cells functions. Thus, since insulin secreted by the pancreas plays a crucial role in maintaining glucose homeostasis, our aim was to determine if sodium arsenite impairs insulin secretion and mRNA expression in single adult rat pancreatic {beta}-cells. Cells were treated with 0.5, 1, 2, 5 and 10 {mu}M sodium arsenite and incubated for 72 and 144 h. The highest dose tested (10 {mu}M) decreased {beta}-cell viability, by 33% and 83%, respectively. Insulin secretion and mRNA expression were evaluated in the presence of 1 and 5 {mu}M sodium arsenite. Basal insulin secretion, in 5.6 mM glucose, was not significantly affected by 1 or 5 {mu}M treatment for 72 h, but basal secretion was reduced when cells were exposed to 5 {mu}M sodium arsenite for 144 h. On the other hand, insulin secretion in response to 15.6 mM glucose decreased with sodium arsenite in a dose-dependent manner in such a way that cells were no longer able to distinguish between different glucose concentrations. We also showed a significant decrease in insulin mRNA expression of cells exposed to 5 {mu}M sodium arsenite during 72 h. Our data suggest that arsenic may contribute to the development of diabetes mellitus by impairing pancreatic {beta}-cell functions, particularly insulin synthesis and secretion.

  7. Arsenite reduces insulin secretion in rat pancreatic {beta}-cells by decreasing the calcium-dependent calpain-10 proteolysis of SNAP-25

    SciTech Connect

    Diaz-Villasenor, Andrea; Burns, Anna L.; Salazar, Ana Maria; Sordo, Monserrat; Hiriart, Marcia; Cebrian, Mariano E.; Ostrosky-Wegman, Patricia

    2008-09-15

    An increase in the prevalence of type 2 diabetes has been consistently observed among residents of high arsenic exposure areas. We have previously shown that in rat pancreatic {beta}-cells, low arsenite doses impair the secretion of insulin without altering its synthesis. To further study the mechanism by which arsenite reduces insulin secretion, we evaluated the effects of arsenite on the calcium-calpain pathway that triggers insulin exocytosis in RINm5F cells. Cell cycle and proliferation analysis were also performed to complement the characterization. Free [Ca{sup 2+}]i oscillations needed for glucose-stimulated insulin secretion were abated in the presence of subchronic low arsenite doses (0.5-2 {mu}M). The global activity of calpains increased with 2 {mu}M arsenite. However, during the secretion of insulin stimulated with glucose (15.6 mM), 1 {mu}M arsenite decreased the activity of calpain-10, measured as SNAP-25 proteolysis. Both proteins are needed to fuse insulin granules with the membrane to produce insulin exocytosis. Arsenite also induced a slowdown in the {beta} cell line proliferation in a dose-dependent manner, reflected by a reduction of dividing cells and in their arrest in G2/M. Data obtained showed that one of the mechanisms by which arsenite impairs insulin secretion is by decreasing the oscillations of free [Ca{sup 2+}]i, thus reducing calcium-dependent calpain-10 partial proteolysis of SNAP-25. The effects in cell division and proliferation observed with arsenite exposure can be an indirect consequence of the decrease in insulin secretion.

  8. Case report: a glucose responsive insulinoma--implication for the diagnosis of insulin secreting tumors.

    PubMed

    Sjoberg, R J; Kidd, G S

    1992-09-01

    Normal insulin secretagogues, including glucose, usually have little influence on insulin secretion from insulinomas. Therefore, insulinomas typically cause fasting hypoglycemia with relative hyperinsulinemia. This report describes a patient with hyperinsulinemia due to an islet cell adenoma with microadenomatosis, which, upon provocative in vivo testing, was found to be profoundly responsive to hypoglycemic and hyperglycemic stimuli. A 72 hr fast followed by brisk exercise resulted in a gradual reduction of serum glucose and insulin concentrations, but did not provoke symptomatic hypoglycemia. Oral glucose tolerance testing resulted in a prompt 10-fold increase in serum insulin accompanied by a mildly symptomatic and gradual fall in serum glucose to 30 mg/dl 90 minutes after glucose ingestion. An intravenous glucose challenge caused an acute increase in serum insulin to more than 1200 microU/ml with a resulting serum glucose of 11 mg/dl 25 minutes later, associated with loss of consciousness. Although a prolonged fast has proven to be the best diagnostic test for insulin secreting tumors, many other provocative tests that use normal insulin secretagogues have been somewhat useful in this regard. The patient in this report supports the concept that insulinomas vary widely in their response to a number of normal physiologic regulators of insulin secretion, including the serum glucose concentration. A variety of provocative tests may be needed to fully evaluate the rare patient in whom there is a strong clinical suspicion of insulinoma but who has a nondiagnostic prolonged fast.

  9. Insulin secretion in the hibernating edible dormouse (Glis glis): in vivo and in vitro studies.

    PubMed

    Castex, C; Tahri, A; Hoo-Paris, R; Sutter, B C

    1984-01-01

    Plasma glucose and insulin have been studied during lethargy and spontaneous arousal of hibernating edible dormouse. During lethargy blood glucose was low while plasma insulin remained at the same level as in other seasons. Plasma glucose and insulin did not fluctuate along the phase of lethargy. During spontaneous arousal plasma insulin rose strongly from the 17 degrees C stage, reaching the higher values at 26 degrees C while blood glucose was only 85 mg/100 ml, then decreased at 37 degrees C. The effect of glucose and temperature on insulin secretion was studied using perfused pancreas preparation from hibernating edible dormice. During the rewarming of the edible dormouse pancreas the insulin release did not occur in response to the absolute extracellular glucose level but occurred in response to a B cell membrane phenomenon which was dependent on the changing rate of glucose level. The effect of glucose and temperature on insulin secretion from perfused pancreas was compared between edible dormouse and homeotherm permanent, the rat. The B cell response to glucose of the dormouse pancreas increased up to 15 degrees C whereas that of the rat only from 25 degrees C. The dormouse insulin secretion reached a peak value at the 30 degrees C of temperature, whereas that of the rat progressively increased until 37 degrees C. These results showed that some biochemical adjustment or process of acclimatization took place in the B cells of the hibernators.

  10. Quercetin Stimulates Insulin Secretion and Reduces the Viability of Rat INS-1 Beta-Cells.

    PubMed

    Kittl, Michael; Beyreis, Marlena; Tumurkhuu, Munkhtuya; Fürst, Johannes; Helm, Katharina; Pitschmann, Anna; Gaisberger, Martin; Glasl, Sabine; Ritter, Markus; Jakab, Martin

    2016-01-01

    Ca2+ in the bath solution. Rutin (50 µM) did not significantly alter the percentage of Annexin-V+ cells, MCV, Akt or Erk1/2 phosphorylation, insulin secretion, or the electrophysiological behavior of INS-1 cells. We conclude that quercetin acutely stimulates insulin release, presumably by transient KATP channel inhibition and ICa stimulation. Long term application of quercetin inhibits cell proliferation and induces apoptosis, most likely by inhibition of PI3K/Akt signaling. © 2016 The Author(s) Published by S. Karger AG, Basel.

  11. Ghrelin but not obestatin regulates insulin secretion from INS1 beta cell line via UCP2-dependent mechanism.

    PubMed

    Chmielewska, J; Szczepankiewicz, D; Skrzypski, M; Kregielska, D; Strowski, M Z; Nowak, K W

    2010-01-01

    The mitochondrial UCP2 mediates glucose-stimulated insulin secretion by decreasing intracellular ATP/ADP ratio. Insulin secretion is a tightly regulated process. Ghrelin, as well as obestatin, were intensively studied to determine their ability to modify insulin secretion. Ghrelin is considered to be an inhibitor of insulin release from pancreatic islets, however little is known about the effects of obestatin. In our study we demonstrate the stimulating effects of both peptides on insulin secretion in INS1 cells. Furthermore, we investigate the potential role of UCP2 in mediating the effects of both peptides on insulin secretion. UCP2 mRNA expression was down-regulated by ghrelin in the presence of 26.4 mM glucose, however it was unchanged after obestatin treatment. Our results confirm that UCP2 could be involved in the stimulating effect of ghrelin on insulin release from INS1 cells.

  12. The cancer-associated FGFR4-G388R polymorphism enhances pancreatic insulin secretion and modifies the risk of diabetes.

    PubMed

    Ezzat, Shereen; Zheng, Lei; Florez, Jose C; Stefan, Norbert; Mayr, Thomas; Hliang, Maw Maw; Jablonski, Kathleen; Harden, Maegan; Stančáková, Alena; Laakso, Markku; Haring, Hans-Ulrich; Ullrich, Axel; Asa, Sylvia L

    2013-06-04

    The fibroblast growth factor receptor 4 (FGFR4)-R388 single-nucleotide polymorphism has been associated with cancer risk and prognosis. Here we show that the FGFR4-R388 allele yields a receptor variant that preferentially promotes STAT3/5 signaling. This STAT activation transcriptionally induces Grb14 in pancreatic endocrine cells to promote insulin secretion. Knockin mice with the FGFR4 variant allele develop pancreatic islets that secrete more insulin, a feature that is reversed through Grb14 deletion and enhanced with FGF19 administration. We also show in humans that the FGFR4-R388 allele enhances islet function and may protect against type 2 diabetes. These data support a common genetic link underlying cancer and hyperinsulinemia.

  13. Cannabinoids inhibit insulin secretion and cytosolic Ca2+ oscillation in islet beta-cells via CB1 receptors.

    PubMed

    Nakata, Masanori; Yada, Toshihiko

    2008-01-10

    Obesity is the main risk factor for the development of metabolic syndrome. Endogenous cannabinoids act on the cannabinoid type 1 (CB1) receptor, a GPCR, and stimulate appetite via central and peripheral actions, while blockade of CB1 receptor reduces body weight in humans. In this study, we aimed to explore a role of the peripheral endocannabinoid system in insulin secretion, which could be important in the metabolic effects of the cannabinoid-CB1 system. We found that mRNA for CB1 receptor, but not CB2 receptor, was expressed in mouse pancreatic islets using RT-PCR. Immunohistochemical study revealed that CB1 receptor was expressed in beta-cells. Furthermore, anandamide and a CB1 agonist, arachidonylcyclopropylamide (ACPA), inhibited glucose-induced insulin secretion from mouse pancreatic islets. Both anandamide and ACPA inhibited glucose-induced cytosolic Ca(2+) oscillation in mouse pancreatic beta-cells. These results demonstrate a novel peripheral action of cannabinoids to inhibit insulin secretion via CB1 receptors.

  14. Proteins altered by elevated levels of palmitate or glucose implicated in impaired glucose-stimulated insulin secretion

    PubMed Central

    Sol, E-ri M; Hovsepyan, Meri; Bergsten, Peter

    2009-01-01

    Background Development of type 2 diabetes mellitus (T2DM) is characterized by aberrant insulin secretory patterns, where elevated insulin levels at non-stimulatory basal conditions and reduced hormonal levels at stimulatory conditions are major components. To delineate mechanisms responsible for these alterations we cultured INS-1E cells for 48 hours at 20 mM glucose in absence or presence of 0.5 mM palmitate, when stimulatory secretion of insulin was reduced or basal secretion was elevated, respectively. Results After culture, cells were protein profiled by SELDI-TOF-MS and 2D-PAGE. Differentially expressed proteins were discovered and identified by peptide mass fingerprinting. Complimentary protein profiles were obtained by the two approaches with SELDI-TOF-MS being more efficient in separating proteins in the low molecular range and 2D-PAGE in the high molecular range. Identified proteins included alpha glucosidase, calmodulin, gars, glucose-6-phosphate dehydrogenase, heterogenous nuclear ribonucleoprotein A3, lon peptidase, nicotineamide adenine dinucleotide hydrogen (NADH) dehydrogenase, phosphoglycerate kinase, proteasome p45, rab2, pyruvate kinase and t-complex protein. The observed glucose-induced differential protein expression pattern indicates enhanced glucose metabolism, defense against reactive oxygen species, enhanced protein translation, folding and degradation and decreased insulin granular formation and trafficking. Palmitate-induced changes could be related to altered exocytosis. Conclusion The identified altered proteins indicate mechanism important for altered β-cell function in T2DM. PMID:19607692

  15. GLP-1 stimulates insulin secretion by PKC-dependent TRPM4 and TRPM5 activation

    PubMed Central

    Shigeto, Makoto; Ramracheya, Reshma; Tarasov, Andrei I.; Cha, Chae Young; Chibalina, Margarita V.; Hastoy, Benoit; Philippaert, Koenraad; Reinbothe, Thomas; Rorsman, Nils; Salehi, Albert; Sones, William R.; Vergari, Elisa; Weston, Cathryn; Gorelik, Julia; Katsura, Masashi; Nikolaev, Viacheslav O.; Vennekens, Rudi; Zaccolo, Manuela; Galione, Antony; Johnson, Paul R.V.; Kaku, Kohei; Ladds, Graham; Rorsman, Patrik

    2015-01-01

    Strategies aimed at mimicking or enhancing the action of the incretin hormone glucagon-like peptide 1 (GLP-1) therapeutically improve glucose-stimulated insulin secretion (GSIS); however, it is not clear whether GLP-1 directly drives insulin secretion in pancreatic islets. Here, we examined the mechanisms by which GLP-1 stimulates insulin secretion in mouse and human islets. We found that GLP-1 enhances GSIS at a half-maximal effective concentration of 0.4 pM. Moreover, we determined that GLP-1 activates PLC, which increases submembrane diacylglycerol and thereby activates PKC, resulting in membrane depolarization and increased action potential firing and subsequent stimulation of insulin secretion. The depolarizing effect of GLP-1 on electrical activity was mimicked by the PKC activator PMA, occurred without activation of PKA, and persisted in the presence of PKA inhibitors, the KATP channel blocker tolbutamide, and the L-type Ca2+ channel blocker isradipine; however, depolarization was abolished by lowering extracellular Na+. The PKC-dependent effect of GLP-1 on membrane potential and electrical activity was mediated by activation of Na+-permeable TRPM4 and TRPM5 channels by mobilization of intracellular Ca2+ from thapsigargin-sensitive Ca2+ stores. Concordantly, GLP-1 effects were negligible in Trpm4 or Trpm5 KO islets. These data provide important insight into the therapeutic action of GLP-1 and suggest that circulating levels of this hormone directly stimulate insulin secretion by β cells. PMID:26571400

  16. Angiopoietin-like peptide 4 regulates insulin secretion and islet morphology.

    PubMed

    Kim, Hyun-Kyong; Kwon, Obin; Park, Kyeong-Han; Lee, Kyung Jin; Youn, Byung-Soo; Kim, Seung-Whan; Kim, Min-Seon

    2017-02-07

    Insulin secretion from pancreatic islet β-cells is primarily regulated by the blood glucose level, and also modulated by a number of biological factors produced inside the islets or released from remote organs. Previous studies have shown that angiopoietin-like protein 4 (Angptl4) controls glucose and lipid metabolism through its actions in the liver, adipose tissue, and skeletal muscles. In this present study, we investigated the possible role of Angptl4 in the regulation of insulin secretion from pancreatic islets. Angptl4 was found to be highly expressed in the α-cells but not β-cells of rodent islets. Moreover, treatment of rodent islets with Angptl4 peptide potentiated glucose-stimulated insulin secretion through a protein kinase A-dependent mechanism. Consistently, Angptl4 knockout mice showed impaired glucose tolerance. In the cultured islets from Angptl4 knockout mice, glucose-stimulated insulin secretion was significantly lower than in islets from wild type mice. Angptl4 peptide replacement partially reversed this reduction. Moreover, Angptl4 knockout mice had dysmorphic islets with abnormally distributed α-cells. In contrast, the β-cell mass and distribution were not significantly altered in these knockout mice. Our current data collectively suggest that Angptl4 may play a critical role in the regulation of insulin secretion and islet morphogenesis.

  17. Insulin secretion is increased in non-diabetic subjects with fasting hypertriglyceridaemia.

    PubMed

    Simental-Mendía, Luis E; Rodríguez-Morán, Martha; Simental-Saucedo, Luis; Guerrero-Romero, Fernando

    2013-03-01

    The elevation of triglycerides is strongly linked with insulin resistance, but it has not been evaluated in relationship to insulin secretion. The aim of this study was to determine whether hypertriglyceridaemia is associated with abnormal insulin secretion. A cross-sectional study was carried out. Eligible subjects, apparently healthy men and non-pregnant women aged 20-65 years were recruited. According to the triglyceride levels, subjects were allocated in the groups with hypertriglyceridaemia and normotriglyceridaemia. Hypertriglyceridaemia was defined by serum triglyceride levels ≥150 mg/dL. Insulin secretion was evaluated by the first phase of insulin secretion (1st PIS) and the second phase of insulin secretion (2nd PIS). A regression linear analysis was performed to evaluate the association between hypertriglyceridaemia (independent variable) and the first and second phase insulin secretion (dependent variables). A total of 247 apparently healthy subjects were enrolled; 113 (45.7%) with hypertriglyceridaemia and 134 (54.3%) in the control group. The simple regression linear analysis showed a significant association between hypertriglyceridaemia and the 1st PIS [B = 207.0; 95% confidence interval (CI) 33.5-380.5, p = 0.02] and the 2nd PIS (B = 48.7; 95% CI 9.2-88.2, p = 0.01). A multiple regression linear analysis adjusted by age, sex, body mass index and waist circumference was performed showing that fasting hypertriglyceridaemia remained significantly associated with the 1st PIS (B = 184.3; 95% CI 13.0-355.7, p = 0.03) and the 2nd PIS (B = 43.1; 95% CI 4.2-81.9, p = 0.03). The results of this study show that hypertriglyceridaemia is associated with the increase of the 1st PIS and the 2nd PIS in apparently healthy subjects. Copyright © 2012 John Wiley & Sons, Ltd.

  18. Lipopolysaccharides-mediated increase in glucose-stimulated insulin secretion: involvement of the GLP-1 pathway.

    PubMed

    Nguyen, Anh Thoai; Mandard, Stéphane; Dray, Cédric; Deckert, Valérie; Valet, Philippe; Besnard, Philippe; Drucker, Daniel J; Lagrost, Laurent; Grober, Jacques

    2014-02-01

    Lipopolysaccharides (LPS) of the cell wall of gram-negative bacteria trigger inflammation, which is associated with marked changes in glucose metabolism. Hyperglycemia is frequently observed during bacterial infection and it is a marker of a poor clinical outcome in critically ill patients. The aim of the current study was to investigate the effect of an acute injection or continuous infusion of LPS on experimentally induced hyperglycemia in wild-type and genetically engineered mice. The acute injection of a single dose of LPS produced an increase in glucose disposal and glucose-stimulated insulin secretion (GSIS). Continuous infusion of LPS through mini-osmotic pumps was also associated with increased GSIS. Finally, manipulation of LPS detoxification by knocking out the plasma phospholipid transfer protein (PLTP) led to increased glucose disposal and GSIS. Overall, glucose tolerance and GSIS tests supported the hypothesis that mice treated with LPS develop glucose-induced hyperinsulinemia. The effects of LPS on glucose metabolism were significantly altered as a result of either the accumulation or antagonism of glucagon-like peptide 1 (GLP-1). Complementary studies in wild-type and GLP-1 receptor knockout mice further implicated the GLP-1 receptor-dependent pathway in mediating the LPS-mediated changes in glucose metabolism. Hence, enhanced GLP-1 secretion and action underlies the development of glucose-mediated hyperinsulinemia associated with endotoxemia.

  19. Isocitrate-to-SENP1 signaling amplifies insulin secretion and rescues dysfunctional β cells.

    PubMed

    Ferdaoussi, Mourad; Dai, Xiaoqing; Jensen, Mette V; Wang, Runsheng; Peterson, Brett S; Huang, Chao; Ilkayeva, Olga; Smith, Nancy; Miller, Nathanael; Hajmrle, Catherine; Spigelman, Aliya F; Wright, Robert C; Plummer, Gregory; Suzuki, Kunimasa; Mackay, James P; van de Bunt, Martijn; Gloyn, Anna L; Ryan, Terence E; Norquay, Lisa D; Brosnan, M Julia; Trimmer, Jeff K; Rolph, Timothy P; Kibbey, Richard G; Manning Fox, Jocelyn E; Colmers, William F; Shirihai, Orian S; Neufer, P Darrell; Yeh, Edward T H; Newgard, Christopher B; MacDonald, Patrick E

    2015-10-01

    Insulin secretion from β cells of the pancreatic islets of Langerhans controls metabolic homeostasis and is impaired in individuals with type 2 diabetes (T2D). Increases in blood glucose trigger insulin release by closing ATP-sensitive K+ channels, depolarizing β cells, and opening voltage-dependent Ca2+ channels to elicit insulin exocytosis. However, one or more additional pathway(s) amplify the secretory response, likely at the distal exocytotic site. The mitochondrial export of isocitrate and engagement with cytosolic isocitrate dehydrogenase (ICDc) may be one key pathway, but the mechanism linking this to insulin secretion and its role in T2D have not been defined. Here, we show that the ICDc-dependent generation of NADPH and subsequent glutathione (GSH) reduction contribute to the amplification of insulin exocytosis via sentrin/SUMO-specific protease-1 (SENP1). In human T2D and an in vitro model of human islet dysfunction, the glucose-dependent amplification of exocytosis was impaired and could be rescued by introduction of signaling intermediates from this pathway. Moreover, islet-specific Senp1 deletion in mice caused impaired glucose tolerance by reducing the amplification of insulin exocytosis. Together, our results identify a pathway that links glucose metabolism to the amplification of insulin secretion and demonstrate that restoration of this axis rescues β cell function in T2D.

  20. Isocitrate-to-SENP1 signaling amplifies insulin secretion and rescues dysfunctional β cells

    PubMed Central

    Ferdaoussi, Mourad; Dai, Xiaoqing; Jensen, Mette V.; Wang, Runsheng; Peterson, Brett S.; Huang, Chao; Ilkayeva, Olga; Smith, Nancy; Miller, Nathanael; Hajmrle, Catherine; Spigelman, Aliya F.; Wright, Robert C.; Plummer, Gregory; Suzuki, Kunimasa; Mackay, James P.; van de Bunt, Martijn; Gloyn, Anna L.; Ryan, Terence E.; Norquay, Lisa D.; Brosnan, M. Julia; Trimmer, Jeff K.; Rolph, Timothy P.; Kibbey, Richard G.; Manning Fox, Jocelyn E.; Colmers, William F.; Shirihai, Orian S.; Neufer, P. Darrell; Yeh, Edward T.H.; Newgard, Christopher B.; MacDonald, Patrick E.

    2015-01-01

    Insulin secretion from β cells of the pancreatic islets of Langerhans controls metabolic homeostasis and is impaired in individuals with type 2 diabetes (T2D). Increases in blood glucose trigger insulin release by closing ATP-sensitive K+ channels, depolarizing β cells, and opening voltage-dependent Ca2+ channels to elicit insulin exocytosis. However, one or more additional pathway(s) amplify the secretory response, likely at the distal exocytotic site. The mitochondrial export of isocitrate and engagement with cytosolic isocitrate dehydrogenase (ICDc) may be one key pathway, but the mechanism linking this to insulin secretion and its role in T2D have not been defined. Here, we show that the ICDc-dependent generation of NADPH and subsequent glutathione (GSH) reduction contribute to the amplification of insulin exocytosis via sentrin/SUMO-specific protease-1 (SENP1). In human T2D and an in vitro model of human islet dysfunction, the glucose-dependent amplification of exocytosis was impaired and could be rescued by introduction of signaling intermediates from this pathway. Moreover, islet-specific Senp1 deletion in mice caused impaired glucose tolerance by reducing the amplification of insulin exocytosis. Together, our results identify a pathway that links glucose metabolism to the amplification of insulin secretion and demonstrate that restoration of this axis rescues β cell function in T2D. PMID:26389676

  1. Free triiodothyronine plasma concentrations are positively associated with insulin secretion in euthyroid individuals

    PubMed Central

    Ortega, Emilio; Koska, Juraj; Pannacciulli, Nicola; Bunt, Joy C; Krakoff, Jonathan

    2008-01-01

    Background Thyroid hormones (TH) may influence glucose metabolism. Hyperthyroid subjects have higher insulin secretion rates when compared with euthyroid individuals. Objective To evaluate the association between TH concentrations and insulin secretion in euthyroid, healthy Pima Indian adults (n=55, 29±7 years, females/males 36/19) with normal glucose tolerance (NGT) admitted to a Clinical Research Unit. Methods TSH, free thyroxine (FT4), 3,5,3′-L-tri-iodothyronine (FT3), and fasting plasma insulin (FPI) concentrations were measured in fasting plasma samples, percentage of body fat (%BF) by dual energy x-ray absorptiometry (DXA), acute insulin response (AIR), and incremental area under the curve (AUC) of insulin in response to a 25 g intravenous glucose tolerance test (IVGTT) and 75 g oral glucose tolerance test (OGTT) respectively and insulin action (M) during an euglycemic clamp. Results FT3 concentrations were associated with FPI, AIR, and insulin AUC both before (r=0.33, P=0.01; r=0.29, P=0.03; and r=0.35, P=0.008 respectively) and after adjustment for age, sex, %BF, glucose (fasting concentrations or glucose AUC), and M (β=0.09, P=0.01; β=0.16, P=0.03; and β=0.24, P=0.0007 respectively). No associations were found for TSH or FT4. Conclusion FT3 was associated with several measurements of insulin secretion in euthyroid individuals with NGT. T3 concentrations may play a role in the regulation of insulin secretion. PMID:18230829

  2. Voltage-gated ion channels in human pancreatic beta-cells: electrophysiological characterization and role in insulin secretion.

    PubMed

    Braun, Matthias; Ramracheya, Reshma; Bengtsson, Martin; Zhang, Quan; Karanauskaite, Jovita; Partridge, Chris; Johnson, Paul R; Rorsman, Patrik

    2008-06-01

    To characterize the voltage-gated ion channels in human beta-cells from nondiabetic donors and their role in glucose-stimulated insulin release. Insulin release was measured from intact islets. Whole-cell patch-clamp experiments and measurements of cell capacitance were performed on isolated beta-cells. The ion channel complement was determined by quantitative PCR. Human beta-cells express two types of voltage-gated K(+) currents that flow through delayed rectifying (K(V)2.1/2.2) and large-conductance Ca(2+)-activated K(+) (BK) channels. Blockade of BK channels (using iberiotoxin) increased action potential amplitude and enhanced insulin secretion by 70%, whereas inhibition of K(V)2.1/2.2 (with stromatoxin) was without stimulatory effect on electrical activity and secretion. Voltage-gated tetrodotoxin (TTX)-sensitive Na(+) currents (Na(V)1.6/1.7) contribute to the upstroke of action potentials. Inhibition of Na(+) currents with TTX reduced glucose-stimulated (6-20 mmol/l) insulin secretion by 55-70%. Human beta-cells are equipped with L- (Ca(V)1.3), P/Q- (Ca(V)2.1), and T- (Ca(V)3.2), but not N- or R-type Ca(2+) channels. Blockade of L-type channels abolished glucose-stimulated insulin release, while inhibition of T- and P/Q-type Ca(2+) channels reduced glucose-induced (6 mmol/l) secretion by 60-70%. Membrane potential recordings suggest that L- and T-type Ca(2+) channels participate in action potential generation. Blockade of P/Q-type Ca(2+) channels suppressed exocytosis (measured as an increase in cell capacitance) by >80%, whereas inhibition of L-type Ca(2+) channels only had a minor effect. Voltage-gated T-type and L-type Ca(2+) channels as well as Na(+) channels participate in glucose-stimulated electrical activity and insulin secretion. Ca(2+)-activated BK channels are required for rapid membrane repolarization. Exocytosis of insulin-containing granules is principally triggered by Ca(2+) influx through P/Q-type Ca(2+) channels.

  3. Glucose-Dependent Insulin Secretion in Pancreatic β-Cell Islets from Male Rats Requires Ca2+ Release via ROS-Stimulated Ryanodine Receptors

    PubMed Central

    Llanos, Paola; Contreras-Ferrat, Ariel; Barrientos, Genaro; Valencia, Marco; Mears, David; Hidalgo, Cecilia

    2015-01-01

    Glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells requires an increase in intracellular free Ca2+ concentration ([Ca2+]). Glucose uptake into β-cells promotes Ca2+ influx and reactive oxygen species (ROS) generation. In other cell types, Ca2+ and ROS jointly induce Ca2+ release mediated by ryanodine receptor (RyR) channels. Therefore, we explored here if RyR-mediated Ca2+ release contributes to GSIS in β-cell islets isolated from male rats. Stimulatory glucose increased islet insulin secretion, and promoted ROS generation in islets and dissociated β-cells. Conventional PCR assays and immunostaining confirmed that β-cells express RyR2, the cardiac RyR isoform. Extended incubation of β-cell islets with inhibitory ryanodine suppressed GSIS; so did the antioxidant N-acetyl cysteine (NAC), which also decreased insulin secretion induced by glucose plus caffeine. Inhibitory ryanodine or NAC did not affect insulin secretion induced by glucose plus carbachol, which engages inositol 1,4,5-trisphosphate receptors. Incubation of islets with H2O2 in basal glucose increased insulin secretion 2-fold. Inhibitory ryanodine significantly decreased H2O2-stimulated insulin secretion and prevented the 4.5-fold increase of cytoplasmic [Ca2+] produced by incubation of dissociated β-cells with H2O2. Addition of stimulatory glucose or H2O2 (in basal glucose) to β-cells disaggregated from islets increased RyR2 S-glutathionylation to similar levels, measured by a proximity ligation assay; in contrast, NAC significantly reduced the RyR2 S-glutathionylation increase produced by stimulatory glucose. We propose that RyR2-mediated Ca2+ release, induced by the concomitant increases in [Ca2+] and ROS produced by stimulatory glucose, is an essential step in GSIS. PMID:26046640

  4. Inhibition of the malate-aspartate shuttle in mouse pancreatic islets abolishes glucagon secretion without affecting insulin secretion.

    PubMed

    Stamenkovic, Jelena A; Andersson, Lotta E; Adriaenssens, Alice E; Bagge, Annika; Sharoyko, Vladimir V; Gribble, Fiona; Reimann, Frank; Wollheim, Claes B; Mulder, Hindrik; Spégel, Peter

    2015-05-15

    Altered secretion of insulin as well as glucagon has been implicated in the pathogenesis of Type 2 diabetes (T2D), but the mechanisms controlling glucagon secretion from α-cells largely remain unresolved. Therefore, we studied the regulation of glucagon secretion from αTC1-6 (αTC1 clone 6) cells and compared it with insulin release from INS-1 832/13 cells. We found that INS-1 832/13 and αTC1-6 cells respectively secreted insulin and glucagon concentration-dependently in response to glucose. In contrast, tight coupling of glycolytic and mitochondrial metabolism was observed only in INS-1 832/13 cells. Although glycolytic metabolism was similar in the two cell lines, TCA (tricarboxylic acid) cycle metabolism, respiration and ATP levels were less glucose-responsive in αTC1-6 cells. Inhibition of the malate-aspartate shuttle, using phenyl succinate (PhS), abolished glucose-provoked ATP production and hormone secretion from αTC1-6 but not INS-1 832/13 cells. Blocking the malate-aspartate shuttle increased levels of glycerol 3-phosphate only in INS-1 832/13 cells. Accordingly, relative expression of constituents in the glycerol phosphate shuttle compared with malate-aspartate shuttle was lower in αTC1-6 cells. Our data suggest that the glycerol phosphate shuttle augments the malate-aspartate shuttle in INS-1 832/13 but not αTC1-6 cells. These results were confirmed in mouse islets, where PhS abrogated secretion of glucagon but not insulin. Furthermore, expression of the rate-limiting enzyme of the glycerol phosphate shuttle was higher in sorted primary β- than in α-cells. Thus, suppressed glycerol phosphate shuttle activity in the α-cell may prevent a high rate of glycolysis and consequently glucagon secretion in response to glucose. Accordingly, pyruvate- and lactate-elicited glucagon secretion remains unaffected since their signalling is independent of mitochondrial shuttles.

  5. The effect of defective early phase insulin secretion on postload glucose intolerance in impaired fasting glucose.

    PubMed

    Sargin, Mehmet; Ikiişik, Murat; Sargin, Haluk; Orçun, Asuman; Kaya, Müjgan; Gözü, Hülya; Dabak, Reşat; Bayramiçli, Oya Uygur; Yayla, Ali

    2005-10-01

    Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) are two risk groups for type 2 diabetes. Type 2 diabetes is characterized by both impaired insulin secretion and insulin resistance but their relative contribution to the development of hyperglycemia may differ due to heterogeneity of the disease. Combined glucose intolerance (CGI), on the other hand, seems to represent a more advanced stage of prediabetes that bears a distinctly higher risk of progression to diabetes and its comorbidities. This study has the aim to compare isolated IFG and CGI categories with respect to the degree of early phase insulin secretion abnormalities and insulin resistance. Subjects who had IFG (fasting glucose: 110-126 mg/dl) were included in the study. A 75-g oral glucose tolerance test (OGTT) with insulin response was done and subjects were classified according to the WHO criteria. Six subjects were excluded because they had diabetic glucose tolerance. A total of 66 patients (53.4 +/- 11.1 years, female/male: 48/18) were divided into two groups according to their glucose tolerance in OGGT (Group 1: isolated IFG and group 2: CGI). Early phase insulin secretion was measured by intravenous glucose tolerance test (IVGTT) and OGTT. Insulin resistance was assessed by the R value of the homeostasis model assessment (HOMA). We did not find any statistically significant difference between groups according to age, gender, body mass index (BMI), fasting glucose, fasting insulin, insulin-AUC (0-180 min) and HOMA-R values. In OGGT there was no statistically significant difference between 0', 30', 60' and 90' insulin levels of the groups; only 120' and 180' insulin levels were higher in CGI than in IFG group (p<0.05). In IVGTT, there was no statistically significant difference between glucose levels of the groups. Furthermore, insulin response to intravenous glucose was higher in IFG than in CGI (p<0.05). Our data demonstrate that isolated IFG and CGI are similar with respect to

  6. Effects of insulin, recombinant bovine somatotropin, and their interaction on insulin-like growth factor-I secretion and milk protein production in dairy cows.

    PubMed

    Molento, C F M; Block, E; Cue, R I; Petitclerc, D

    2002-04-01

    , which were 122.5, 181.3, 342.3, and 492.2 ng/ml for saline, insulin, rbST, and insulin combined with rbST, respectively. In conclusion, these results clearly demonstrated that insulin interacts with bST in early lactation to improve milk protein synthesis and yield in dairy cows. These effects are probably mediated through a combination of bST nutrient mobilization, bST-induced gluconeogenesis, bST-induced insulin peripheral resistance, and bST/insulin synergism on insulin-like growth factor-I secretion and on mammary epithelial tissue.

  7. The importance of early insulin secretion and its impact on glycaemic regulation.

    PubMed

    Garber, A J

    2000-09-01

    Type 2 diabetes is characterised by a progressive deterioration of the prandial insulin response, in a situation of continuing insulin resistance. Early phase insulin release is attenuated and delayed and there is a consequent failure to suppress glucagon secretion and curtail hepatic glucose production and gluconeogenesis. Postprandial plasma glucose concentration rises to pathological levels and fails to return to normal before the patient consumes their next meal, creating a problem of continuous daytime hyperglycaemia. Although late insulin secretion is preserved it does not rectify the hyperglycaemia. The pathology of excessive prandial glucose excursions and continual daytime hyperglycaemia can be normalised, at least in part, if early-phase insulin availability is restored through pharmacologic intervention. Initially, the feasibility of this approach was demonstrated experimentally with the use of carefully controlled insulin infusions or insulin analogue injections. More recently, the availability of the rapid or early augmentor of insulin secretion--repaglinide--provides a means for restoring prandial glucose regulation with oral therapy. Placebo-controlled and oral hypoglycaemic agent (OHA) comparative studies of repaglinide have established its antidiabetic efficacy and flexible mealtime/dosing studies have confirmed the importance of the prandial approach to treatment. Prandial glucose regulation with repaglinide has also been demonstrated to provide synergies when used as combination therapy with insulin sensitising agents. As a strategy, prandial glucose regulation has a number of theoretical advantages over the use of fixed doses of conventional insulin secretagogues, and these have been borne out in clinical trials. As well as offering a more flexible approach to treatment, prandial repaglinide is associated with a reduced risk of severe hypoglycaemia.

  8. SGK1 dependence of insulin induced hypokalemia.

    PubMed

    Boini, Krishna M; Graf, Dirk; Kuhl, Dietmar; Häussinger, Dieter; Lang, Florian

    2009-02-01

    Insulin stimulates cellular K+ uptake leading to hypokalemia. Cellular K+ uptake is accomplished by parallel stimulation of Na+/H+ exchange, Na+,K+,2Cl- co-transport, and Na+/K+ ATPase and leads to cell swelling, a prerequisite for several metabolic effects of the hormone. Little is known about underlying signaling. Insulin is known to activate the serum and glucocorticoid-inducible kinase SGK1, which in turn enhances the activity of all three transport proteins. The present study thus explored the contribution of SGK1 to insulin-induced hypokalemia. To this end, gene-targeted mice lacking SGK1 (sgk1-/-) and their wild-type littermates (sgk1+/+) have been infused with insulin (2 mU kg(-1) min(-1)) and glucose at rates leaving the plasma glucose concentration constant. Moreover, isolated liver perfusion experiments have been performed to determine stimulation of cellular K+ uptake by insulin (100 nM). As a result, combined glucose and insulin infusion significantly decreased plasma K+ concentration despite a significant decrease of urinary K+ excretion in sgk1+/+ but not in sgk1-/- mice. Accordingly, the plasma K+ concentration was within 60 min significantly lower in sgk1+/+ than in sgk1-/- mice. In isolated liver perfusion experiments, cellular K+ uptake was stimulated by insulin (100 nM), an effect blunted by 72% in sgk1-/- mice as compared to sgk1+/+ mice. Accordingly, insulin-induced cell hydration was 63% lower in sgk1-/- mice than in sgk1+/+ mice. Moreover, volume regulatory K+ release was 31% smaller in sgk1-/- mice than in sgk1+/+ mice. In conclusion, the serum and glucocorticoid-inducible kinase SGK1 participates in the signaling mediating the hypokalemic effect of insulin.

  9. Heterozygous SOD2 Deletion Impairs Glucose-Stimulated Insulin Secretion, but Not Insulin Action, in High-Fat–Fed Mice

    PubMed Central

    Dai, Chunhua; Lustig, Mary E.; Bonner, Jeffrey S.; Mayes, Wesley H.; Mokshagundam, Shilpa; James, Freyja D.; Thompson, Courtney S.; Lin, Chien-Te; Perry, Christopher G.R.; Anderson, Ethan J.; Neufer, P. Darrell; Wasserman, David H.; Powers, Alvin C.

    2014-01-01

    Elevated reactive oxygen species (ROS) are linked to insulin resistance and islet dysfunction. Manganese superoxide dismutase (SOD2) is a primary defense against mitochondrial oxidative stress. To test the hypothesis that heterozygous SOD2 deletion impairs glucose-stimulated insulin secretion (GSIS) and insulin action, wild-type (sod2+/+) and heterozygous knockout mice (sod2+/−) were fed a chow or high-fat (HF) diet, which accelerates ROS production. Hyperglycemic (HG) and hyperinsulinemic-euglycemic (HI) clamps were performed to assess GSIS and insulin action in vivo. GSIS during HG clamps was equal in chow-fed sod2+/− and sod2+/+ but was markedly decreased in HF-fed sod2+/−. Remarkably, this impairment was not paralleled by reduced HG glucose infusion rate (GIR). Decreased GSIS in HF-fed sod2+/− was associated with increased ROS, such as superoxide ion. Surprisingly, insulin action determined by HI clamps did not differ between sod2+/− and sod2+/+ of either diet. Since insulin action was unaffected, we hypothesized that the unchanged HG GIR in HF-fed sod2+/− was due to increased glucose effectiveness. Increased GLUT-1, hexokinase II, and phospho-AMPK protein in muscle of HF-fed sod2+/− support this hypothesis. We conclude that heterozygous SOD2 deletion in mice, a model that mimics SOD2 changes observed in diabetic humans, impairs GSIS in HF-fed mice without affecting insulin action. PMID:24947366

  10. INSULIN-INDUCED GLOMERULOSCLEROSIS IN THE RABBIT

    PubMed Central

    Mohos, Steven C.; Hennigar, Gordon R.; Fogelman, John A.

    1963-01-01

    An attempt has been made to induce intercapillary glomerulosclerosis in rabbits by immunization with insulin incorporated in Freund's adjuvant and followed by repeated challenges with subcutaneously given insulin. It was observed that lesions resembling human diabetic glomerulosclerosis with occasional nodule-like formation could be produced and that the challenge insulin injections produced proteinuria. The presence of a delayed type of hypersensitivity seemed necessary for the lesions to occur as did the dissemination of the immunizing material to the kidneys. The experiment also disclosed that intravenously given DIS-tagged insulin localizes in a subtly different kind of glomerular lesion with different staining properties. The significance of these findings and the possible role of insulin treatment in the pathogenesis of human diabetic glomerulosclerosis is discussed. PMID:14087614

  11. The role of pancreatic insulin secretion in neonatal glucoregulation. I. Healthy term and preterm infants.

    PubMed Central

    Hawdon, J M; Aynsley-Green, A; Alberti, K G; Ward Platt, M P

    1993-01-01

    The glucoregulatory role of insulin in adult subjects is undisputed. However, less is known about the secretion of insulin and its actions in the neonatal period, either for healthy subjects, or for those at risk of disordered blood glucose homoeostasis. The relationships between blood glucose and plasma immunoreactive insulin concentrations were therefore examined in 52 healthy children (aged 1 month-10 years), 67 appropriate birth weight for gestational age (AGA) term infants, and 39 AGA preterm neonates. In children and AGA neonates, plasma immunoreactive insulin concentration was positively related to blood glucose concentration. However, although both groups of neonates had significantly lower blood glucose concentrations than children, plasma immunoreactive insulin concentrations were significantly higher in both term and preterm neonates, when compared with children. The variation in plasma immunoreactive insulin concentrations was greater for neonates than for children. These data suggest, that compared with older subjects, plasma immunoreactive insulin concentrations are high in newborn babies and that neonatal pancreatic insulin secretion is less closely linked to circulating blood glucose concentrations. There are important implications for the interpretation of studies in hypoglycaemic and hyperglycaemi